Why logic puzzles make good interview questions January 10, 2007
Posted by Imran Ghory in job interviews, recruitment.trackback
Logic puzzles in interviews seem to be one of those things that everyone either loves or hates, but speaking as an interviewer I find logic questions critically important in deciding between candidates – far more than “behavioural” or “situational” type questions that HR peeps seem to favour.
My aim in this post is to convince those of you that hate them, that they are actually useful questions to ask (and be asked) and give everyone else an insight why interviewers especially at big tech companies seem to love this type of question.
To begin with I feel I should draw a separating line between logic puzzles and brain teasers. Logic puzzles are of the type where there’s no “trick” but rather puzzles which have answers that can be logically deduced. Often these are puzzles where there are a number of different valid solutions but you’re asked to find the optimal solution, examples of this type of question include the Rope Bridge and The Orb.
Brain teasers however often have a “trick” – something unusual you have to guess often about the assumptions of the problem. While these can provide some insight into the candidate I think their value is limited, and that they’re far weaker than pure logic puzzles.
I’d like to show what an interviewer can find out about a candidate from a logic puzzle via an example, walking through an interviewer asking the question and showing how various canidates respond:
Interviewer: Imagine you have eight coins, seven of which weigh the same and one that doesn’t (it’s heavier). You need to use a pair of scales to find out what’s the odd one out.
If this seems familiar it probably is, this is apparently one of the most asked logic puzzles in the known universe. It’s used in interviews by Microsoft, Amazon, Google, and probably hundreds of other firms. It’s also in pretty much every book on the topic and on dozens of websites. Now for some example responses:
Candidate Alice: What’s a pair of scales ?
Candidate Bob: How much heavier is the other coin ?
Candidate Carol: Well you could weigh them one-by-one until you find the pair which is uneven, and then….
All of the above responses are good, both Alice and Bob recognized that they had been given a problem they didn’t fully understand so they took the step of asking relevant questions to clarify the problem in their own mind before trying to solve it.
This is a situation that occurs frequently in intellectually demanding jobs, people are frequently asked to solve problems for others. Everyone has different experience and background and will understand the problem differently. This a major advantage, in a team diversity will help you come up with new solutions to a problem. However it also means that everyone will interpret the problem differently, and asking question to clarify what the problem is can be a key part of ensuring everyone’s on the same page.
Carol’s right too, she’s come up with a valid solution right-off-the-bat, it’s not the optimal solution but it is a correct one. We can discuss it and see if she can improve it.
Now a bad response:
Candidate Dan: I don’t know.
If the only purpose of asking logic questions was to catch people who gave this answer, then they’d still be worth asking. This is a candidate you never want in your team. I have three hypothesis about Dan-esqe candidates,
- They really can’t solve the problem at all
- This indicates the candidate struggles with problems which intelligent 5 year-olds can solve, not a good sign.
- They can’t be bothered to try
- Not a good sign of motivation
- They don’t want to answer it
- If they can’t explain why the don’t want to answer the question then their communication skills are probably too weak. In most jobs refusing to do something without giving any reason is likely to be unconducive to a good working environment.
Luckily all three are grounds for rejecting a candidate so interviewers don’t have to think too hard about which the candidate falls into.
So lets look at the next stage of this response, where the candidate has understood the problem and has come up with the trivial solution that Carol has above.
Interviewer: Yes that would work, how many times would you have to use the scale to find the solution using that method in the average and worst case ?
Candidate Carol: Four and eight respectively
Interviewer: Are you sure about that ?
Candidate Carol: hmm, four and ten ?
Carol’s initial response is both a good and bad answer, Carol managed to correctly estimate the average and worst times, showing an understanding of how the speed of the solution depends quite a lot on luck. However her answers aren’t the exact correct values, and worse still when she’s challenged she come’s back with a worse answer indicating that maybe she just guessed.
At this point the interviewer might start to push her on how she got those numbers, if it turns out she starts wildly guessing answers while under pressure, she might not be suitable for a work environment which is pressure heavy and detail-critical.
But now lets move on:
Interviewer: So can you think of a better solution to this problem which lets you use the balance fewer times ?
Candidate Errol: You can split the coins in half. weigh them against each other, throw away the lighter ones, and repeat until you only have one left.
This is a good answer, I’d expect anyone coming from a Comp Sci or Maths background to get this far without any help. People from other backgrounds I might nudge in the right way and see if they can find the solution.
However if you’re from the first group and don’t get this solution I’d be a little worried, it wouldn’t be an instant reject but it’d definitely be a question-mark. Maths/Comp Sci people should have seen similar methods of tackling problems as part of their studies, and should be able to reason about this problem from their previous experiences.
If the candidate came straight to this solution skipping the obvious solution then I’d ask them about the average/worst times for this solution instead. But otherwise back to improving:
Interviewer: Do you think this is the best solution ?
Candidate Fred: I think it is
Interviewer: (smiling) I’ll give you a clue, it isn’t.
Interviewer: You’ve come up with solutions balancing one-against-one and four-against-four, what else can you do ?
Candidate Fred: Three-and-Three ?
Interviewer: What do you learn if you do that ?
Candidate Fred: Which three is heaviest
Interviewer: What if the scale is balanced ?
Candidate Fred: The heavy coin must be one of the other two — you can split the coins three ways every time.
Interviewer: Yep, that’s the optimal solution, do you know for N coins how long it’ll take ?
Candidate Fred: About Log N
Interviewer: What base ?
Candidate Fred: Base 3
That’s typically how the best solution is arrived at by a good candidate. How much help I give the candidate depends how much they’re struggling, some candidates just click about going through the other combinations and come up with the answer. Some like Fred manage to come through with a little help, some candidates just get stuck. I think you can guess which order I want to hire those candidates.
And for bonus points:
Interviewer; Can you prove it’s the optimal solution ?
Candidate Goyle: No I’m not sure how, but I’m fairly sure it is.
Candidate Hermione: Each weighing gives you three pieces of information (if the left side is heavier, if it’s balanced, if the right side is heavier), that is one trit (trinary bit) of information. As the heavy coin can be anyone of the N you need at least enough trits to give N outcomes. Which means you need at least log3 of N goes, which happens to be how many our solution takes. So there can’t be a solution better than the one we discussed.
I don’t really expect a candidate to be able to answer this, but it’s a good sign if a candidate can. People who are solid on the practical side but can excel on the theoretical side as well are rare indeed and it’s well worth identifying them.
So hopefully that’s shown you that there’s a lot of information about the candidate that an interviewer can get by asking a logic question. The interviewer doesn’t just want the candidate to show off their intellect by coming up with the correct answer. They want to see the process by which the candidate got to that answer, as that process is likely to be one that the successful candidate will have to go through frequently during their job.
If you’re interested in learning more about this sort of logic puzzle I’d recommend Moving Mount Fuji (the book; not the task) which gives a good history of how logic puzzles became a part of corporate interviewing. If you’re an (ex)student looking for your first job in the tech sector I’d recommend Programming Interviews Exposed which gives lots of logic and programming questions which are typical in technical interviews.
Imran On Tech 
Your analysis is good, the problem is that everyone already knows these problems. So in the “real” world (that is, in the world as I see it, a differently wrong vision than how you see it) you are actually testing to see if the person has read up on how to interview. By using the known questions you actually mask the smart person who has not read up on the question, but figures out the answer.
When I used to sit the Command Boards in the Navy to determine who would become the Commnading Officer of a ship, questions like these were very common.
They were very useful.
Have you found that better puzzle solvers actually make better employees (for whatever position you presumed to be filling here)?
Or, are you just assuming that to be so?
If a candidate did as you suggested and read lots of logic questions, in order to be more prepared for your interview, would that turn them into a better employee?
Better than situational questions? I think all three types compliment each other, but the most important is trying to simulating the actual job.
A number of colleagues of mine like using logic puzzles in interviews, but I completely disagree.
It’s not really logic problems in and of themselves that I’m opposed to, but rather the idea that an interviewer can evaluate another person’s analytical abilities in an interview setting via some talk-aloud protocol.
Perhaps to some, asking logic questions has nothing to do with assessing logical ability, and more to do with judging motivation or communication skills, or ability to stay cool under pressure. In that case, great. But if the goal is to discern a person’s adeptness at solving complex logic problems, I think interview logic questions are only tenuously correlated.
First of all, people get nervous in interviews, plain and simple. When they’re nervous, they don’t think as clearly. Just because someone gets flustered solving a problem in an interview does not mean that person isn’t a great mathematician, logician, developer, etc. Now, if part of the job is to think in pressure social situations, well that’s a different story.
Second, I don’t think we are even privy to how we solve logic problems, so I’m not sure an interview can. The cognitive processes we use for solving problems are not really accessible to our conscious self, it’s only after the solution has popped into our head that we try to give some post hoc rationalization for how we reached this solution. Truth is, we don’t really know. Some great mathematicians have a very difficult time explaining how they solve what they do. See Dennett’s “Consciousness” for some interesting thoughts on this. Basically, this whole notion of “explaining how we think” through some talk-aloud protocol is built on a gross (but common) misapprehension of our own consciousness.
Lastly, I think it’s rather presumptuous to think that an interviewer, with no formal training in psychology, will be able to evaluate a person’s analytical skills in a 30-60 minute interview. There are much better measures, if this is what you’re trying to measure. If someone graduated from Princeton and had great GRE scores but had a bad interview, what would you think? Most would favor their own judgement, and this is a common decision foible (decision theory has much to say about this).
I have taught college level for over 12 years, and worked in the real world for over 14. I also have a psychology academic background, so am familiar with the world of theoretical and practical thoughts processes. Your well thought out and on the mark response is one of the most profound and legitimate ones. Especially on the notion that an interviewer with unknown background in relevant science can be assumed to have such credibility to be accurate in their assessment. My experiences in the real world prove 90% of all this support for logical questions to be full of more gobbledygook then anything else. I totally agree with you that like every job interview, watching the person ar work for a few days after being hire will unscramble the theory from reality. Fact is that I have seen some of my best employees turn out to have been the lesser impressive ones on interviews. Why? Because in many cases these questions ignore the abilitity of some people to excel in real world problem solving versus academic test games. This reminds me of the fallacies behind the use of credit scores to determine the most responsible workers. What a joke. I had this one lady with horrible credit scores, who was so effective..that she became my right hand person on the team. Fact is there are too many unknowns for an interviewer to give too much weight to these questions. That lady had bad credit because her husband embezzled her financials, impacting her credit. I saw pass her credit score by engaging her in real life scenarios of our business and I was amazed at her abilities to think through valuable solutions. Things these logical questions fail to pick up. I am not totally against logic questions. I am against how they are being loosely used by wanna-be psychologist interviewers.
I’d walk out of the office. Not worth it. So I guess the questions do work.
I agree with you that logic puzzles are a great way to determine a potential employee’s problem solving abilities; however, this is only one facet of the overall worker’s aptitude to problem solve. More and more, employers are looking for candidates who demonstrate a balance between both logical and emotional intelligence. EQ consists of many skills today’s employers are demanding in their workplaces: self-awareness, initiative, empathy, impulse control, stress management, and leadership. As our global communication technology grows, so will the global workplace for most businesses-connecting new coworkers around the globe. This is why more interviews for management level positions include EQ tests.
One past employer wanted to know how I resolved a conflict between a coworker. He also wanted to know how well I had worked in a team environment, citing specific examples. I have also had a few bosses who could have learned a thing or two when dealing with their employees directly. These superiors were hired, in my opinion, before EQ was a criterion.
Sure I could be an Aristotle and solve your logic puzzles all day, but in the real world this was just one of the skills which I was asked to show during my last job interview.
rstangland I agree with you, logic puzzles should only be a small part of the overall interview. But if I had to get rid of part of an interview I’d get rid of behvaioural questions over logic questions, from my experience it’s too easy for someone who’s good with words to bluff them. I’ve seen to many candidates who can talk the talk but can’t walk the walk.
This is excellent information. I’ve done a ton of interviewing for technical and leadership positions, but have never used a logical question. I’ll be sure to research some more obscure examples since this is the one most know about. Will add it to my mix.
Ben Northrop – I agree with you that one interview cannot possibly tell you everything you should know about a candidate. However I think this is a great way to find out how a candidate will handle the problem. While there is an optimal answer, and obviously a wrong answer, there are many right answers. It provides a window into their style of solving problems (same thing with behavioral and situational questions). Are they guessing? Detailed? Confident? Innovative? Efficient? Do they internalize the process? Verbalize it? Ask to go to the whiteboard? All complex problems break down to simpler pieces. And I think giving them an out because they are nervous is providing them a crutch. Everyone gets nervous – they should be able to handle it. Plus, that’s why it’s good to have several interviews, preferably on different days, to see what patterns come up.
The opportunity to ask the “Are you sure?” question is very important. I don’t really care how you get there.
(In a course I am teaching, where students are required to make lists, the equivalent question is “Are you done? How do you know?”
Jonathan
Yeah that all makes sense. Its also a good way to see how people think on their feet.
http://falcons28.wordpress.com/
If your looking for someone to at least try to answer the question to show motivation, then I will do well. As for providing the correct answer, then I’m doomed. I will also need a huge dry erase board and lot’s of colored pens to work on my answer. I don’t do well with these things on the spot, even though I got A grades in my college logic class and also my statistics course. Go figure.
Kathleen if you at least try to answer any question that is being asked by an uncertified scientist …and just another employee on the team….I would hire you….but mostly for other stronger job relevant reasons. The problem here is not the questions, but rather their loosely usage by wanna-be psycho-social scienctist. Not to sound controversial, but for some reason…..I have noticed more and more interviewers using these questions to be people coming here with programming or similar logical oriented types of degrees from back home (no pond intended). In the US, these kinds of questions are heavily used by the military and by scientific organiizations….where the interviewers tend to be trained to assess responses to these questions. But their used in other business settings (I.e., IT related jobs or depts) is not only intellectually biased, but leads to miscalculations in not hiring great workers. I say this with credibility in the science of personal assessments coupled with having worked in IT for the last 10 yrs. Bottomline…. If you don’t have the credentials in the science behind logical thinking and cognitive personality testing, you should thread lightly on these types of questions….otherwise you might be setting yourself up for making rash irrational and baseline hiring decisions. In essence, if you play the piano but you’re interviewing someone for a bookkeeping position, then stick to accounting questions and stop trying to use piano playing questions to judge the prospective employee…no matter how much you’re itching to ask such irrelevant questions. But, if you are interviewing for a position at the CIA or CDC, then by all means go with a flood of these questions.
I agree with M. Knot Konvinced: I’m not sure that someone adept at answering these kinds of questions will automatically be a good employee. I suspect it could be more of a measure of how well a person does under pressure – and if you’re in a high-pressure environment, then that might be one thing you want to measure. However, I know a lot of people (myself included) who just freeze up whenever an interviewer starts asking these kinds of questions – after so many interviews it’s become a conditioned response now.
Better: Give the interviewee a question that is relevant to the job being interviewed for. If it’s a coding problem give them a laptop (if they didn’t bring one) that has development tools on it, explain the problem, make sure the candidate understands it and then leave the room for 15 or 20 minutes. Have them code on a laptop as opposed to on the whiteboard (writing code out by hand uses completely different parts of the brain than does typing code into an editor). Best interview (and best interviewer) I ever had did this. It was so much better than standing at a whiteboard with a marker in my hand while an interviewer barks questions about this or that aspect of the code being written.
Good point, Imran.Examination of logical thinking is always a key component of multi-stage selection processes, and it is indeed tough to make an exam for this.On the spot surprizes like these test your toughness and ability to react as well, not just logical thinking.
It makes more sense to me to ask questions related to the job. My coworkers and I used to toss logic problems back and forth, but that had nothing to do with our job. In the interview, my potential boss actually wrote some problems on a board and asked me to write code to solve them. That’s far better information about how well I can work in this situation than a logic problem is – it demonstrates problem solving skills AND knowledge about the topic. I think interviews should contain active sessions where the interviewee demonstrates their skill.
If they were interviewing for Sr. Logic Problem Solver, these questions would be relevant.
[…] January 11, 2007 @ 4:35 am } · { Modern Science } Recently, Imran on Tech ran an article on logical puzzle on job interviews. Logical puzzles are often posted to interviewee […]
[…] January 11, 2007 at 12:12 am | In Staffing | Over at Imran on Tech there’s a great post about the value of using logic questions in the interview process. I couldn’t agree more. In addition to situational and behavioral questions this is a […]
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The Snow Words Myth: Progress at Last How many words do Eskimos really have for snow? (tags: Language) Why…
The LAST thing I want is a programmer who thinks that putting “trinary bits” in programs is a good idea. I would guess that 95 out of every 100 lines of code would be better off written in a simpler, more readable way, than using clever “tricks” or “shortcuts” that may or may not bring an increase in speed.
What I want when I hire a programmer is somebody who can come up with the least complicated solution to a given problem, because their solution is going to be in the code base a long time – probably over 5 years – and will be reviewed, investigated, and debugged by numerous people. The more confident I am that the code will be understandable by others, the happier I am.
One more thing: when interviewing, there is very little point in putting a candidate on the spot and asking for a complete solution to a problem that the interviewer already has written answers to.
Much better to take along a problem that is a genuine work-related problem, and attempt to solve it together. You can test technical skills, problem-solving, communication and teamwork in a positive, non-confrontational way.
What about the random interview questions along the lines of “how many cows are there in the world?”, or “why don’t cows laugh?” (sorry about the temporary cow obsession, it will pass). This requires some general knowledge, some logic, some intelligent guesswork, and a lot of thinking on your feet – you can’t prepare for this sort of thing.
mapsadaisical – how many cows are there in the world? is that a logic puzzle?
I know someone who just interviewed for a non-tech position and was asked “why are man hole covers round?”
she didn’t know, but tried to answer, saying “the round shape is better for people to get in and out of the holes” (meaning: they fit through the holes better)
The interviewer told her that she was the only person to even attempt answering the question, and that he thought her answer was pretty good.
I think the best answers to that question are :
1. round covers can’t fall through the hole if dropped – square ones could if turned diagonally.
2. being round allows workers the luxury of rolling them into position rather than carrying them around since they’re so heavy
awesome article. I’m definitely bookmarking this. Thanks so much!
Great article on a number of counts:
1. Helpful to (believe it or not) a majority of those who interview and are interviewed who have never run up against these types of questions.
2. Love the insight about needing to know that people are on the same page as they tackle a problem. You’re right when you say that people regularly have a different perspective on what the problem IS, which then taints their ability to thrash about before coming to solution. Most people go straight from their perception of the problem to a solution, without taking the time to make sure there is clear understanding all around.
The best interview question I’ve ever been asked is similar to the manhole question. It was, “If you could pick up Pikes Peak (I’m in Colorado and Pikes Peak is our nearest 14,000+ mountain) and weigh it, how would you go about doing it?”
There was no right or wrong answer. They were looking for how you tackle a problem, how you make decisions, whether you go it alone, or bring in others to help you.
My response was this:
1. You’d have to tell me where you want to draw the boundaries of the mountain. We’re at about 6000 ft. in Colorado Springs, so do we start measuring from sea level or from the altitude where the foothills begin?
2. Do you want it measure in the winter, when it’s packed with tons of ice and snow, or in the summer?
3. Are we going to weigh anything that happens to be on the mountain at the time, including hikers, campers, boaters and oh yes, the squirrels! (I was being a little too cute for my own good!)
4. I’d get a geological survey to determine the percentage of granite, soil, etc.
5. I’d need to then calculate those percentages and multiply out the mass of each type of materials.
Blah, blah, blah. I got the job. It was the wrong job for me, which is why I’m now self employed. haha! But it was a great question. You can substitute Pikes Peak for the Mississippi River or other geographical landmarks close to your location.
Finally, I’d like to introduce The CARLA Concept(TM) to assist with this type of problem solving process. It is a simple model based loosely on your 6th grade scientific method. People do use it in interviews, to help get teams talking, to debrief the boss, to do a gap analysis, etc. Here it is and please use it freely (with attribution please):
C – what circumstances/challenge/change are we facing? (Here’s where being clear about the nature of the challenge/problem comes in. It forces folks to discuss, dissect and get to common understanding)
A – what actions did we take in the past? (Or what actions do we plan to take in the future?)
R – what results did we achieve? (Or, what results do we hope to achieve in the future?)
L – what lessons did we learn? (Lessons learned are crucial so we don’t make the same mistakes over again, so we learn how to do it differently/better in the future.)
A -another option or alternatives for the future, now that we know what we know.
A great book I’m reading right now is “The Wisdom of Crowds” by James Surowiecki that explores how the group is usually smarter overall than even the professed “experts”. Great read.
Great article! Good thought provoking material. I’ll share on my blog, newsletter, etc. Thank you!
Laura Benjamin
Oxi – you allude to an excellent point – there is no single magic question that will unveil whether a candidate makes a good employee. This would be another data point. And directing questions and tests that directly impact the job they are interviewing for is a must. As is discussing how their past experience relates to this opportunity. A well rounded interview, and several of them in fact, is a must.
The burden is also on the interviewer to help the candidate give their best interview and position these types of questions so that they don’t have the appearance of a trick question. You don’t want to give the impression that the interview really boils down to this.
Aside from the technical ability and aptitude, an interview should give some indication as to what type of environment, including management style, will allow the candidate to thrive and do their best work. You want to know what you need to do to make sure they are successful. Unfortunately most interviewers I’ve known don’t tend to think like that.
This is a very good post. I’ve just recently begun interviewing candidates and this post gives me some aspects of the conversation worth thinking about. Well written and thanks!
Having recently interviewed a number of candidates, I think that the most useful thing logic questions weed out the people who say, “I don’t know,” and leave it at that. Over half of the candidates fell into that group! The good news is that you don’t need logic problems to track down the candidates that give up easily. My guess is that any task that requires some thought would do the trick. For example, I had candidates look over some very badly written code and provide feedback. “I’d have to see it in action,” is not a good answer.
This is part of the reason I don’t have patience for logic and math problems and the people who think they’re windows to our souls. As hard as the people who write them try to make them realistic, they never are.
The Rope Bridge: “they only have one flashlight and it only has enough light left for seventeen minutes.”
Enough light left? Is it a glow-in-the-dark based flashlight? Surely you mean it has enough power. Charge. Something. It doesn’t just have a cup of photons contained within it’s casing which it continually releases, does it?
If you’re going to ask me this question in an interview, I’m going to give you the REAL answer:
To know that the flashlight only has “enough light” for seventeen minutes, you must be carrying either a battery meter or some device which tests the life of a light bulb. What are you doing out in the woods with such equipment? That’s extra weight, throw it away. Furthermore, everyone knows that when batteries fail, you can get a few extra minutes out of them if you wait a bit, roll them around in your hands, and switch their order in your device. If that still does not make you fast enough, it’s time to give some motivational speaking to the “slowpoke” (which, by the way, is not a very team-oriented nickname to give someone who represents 25% of your squad). Also, since the “slowpoke” is so slow, does that mean s/he is more dangerous? If he is more at risk of injury, we may need to send him first, in order to make sure we have light left for wound dressing or emergency rescue.
Which points us to two facts: if you needed an emergency rescue, you would light a fire (And, if you’re having this much trouble getting four people back to camp before you run out of light, you shouldn’t be out there in the first place and you *do* need rescued). So why don’t you light a fire? Torches. One on either side of the bridge if you don’t know how to make a torch.
Finally, assuming we know the bridge-crossing times from our outbound journey, who got us back to the bridge with not one second to spare? This question is supposedly to see whether the interviewee can function under pressure – how do you think Slowpoke is going to do knowing that if he takes one slightly smaller step over the bridge, we all die? He’s going to go even slower. Or fall. I guess since I’m determining who crosses when, I’m the leader, and therefore responsible for this situation. Which means you shouldn’t hire me, because I don’t really understand deadlines.
Please, interviewers, if you’re going to get tricky, make sure you’re smarter than the one you’re trying to trick.
You’ve hit on one of the real reasons why this type of question is used in an interview… Only people who interview regularly will be “up to speed” on the latest interview “tricks” used to put the interviewee in an uneasy state. I have not interviewed very many times in my 50+ years but it doesn’t take me too long to figure out whether a person is trying to find out what I know or just trying to make me uncomfortable. I’m not very interested in working for a person who would intentionally make an interviewee sweat, so I try to have a little fun of my own…
Good post, I think the interesting part of things like logic puzzles is watching how people respond and how they work their way through it – more interesting than getting to the answer for most jobs.
I think that the simple fact that you are advising people to read a book called “Programming Interviews Exposed” shows that these kind of questions can be flawed.
I have a bunch of friends who were really big in programming competitions and can solve all these kinds of problems presto. One of them would only work on something that he felt like working. So when it was report writing time he always wrote miserably and was always late. Another one just cared about solving “hard” math problems, his code was a complete and total mess. Your questions would highly rank them.
Your logic questions also miss the point that by being from different social backgrounds some people are ashamed of getting something wrong in the face of a stranger. This will make them hesitate much more.
Go and read Joanna Rothman for some counter opinions to this logic problem interviewing style. (Sorry can’t find link immediately.
I don’t think giving the candidate a puzzle to solve is a good interview practice. Yes, you can weed out the candidates who don’t even want to think – but, at the same time, you will also weed out the ones who just aren’t good puzzle solvers. Solving a puzzle under time pressure and in a stressful environment requires skills which might be useful under some conditions, but, most probably, are not relevant to the position.
I think that giving puzzles is a part of “find somebody who’s smart the same way I am” pattern. I personally prefer asking more job-related questions, and checking important fundamental knowledge.
ya logical questions are always ask in interviews, this is because
they wanna test your real suituation handeling power..!!
what ans you gave to that question doesn’t matter the thing which matters is your logic behind that ques..!!
All MNC’s use logical ability test because they wanna test weather you are able to face real suituation or not..!!
In almost all companies you have to deal with real word problem.
But the main thing is >>
In interviews nervesnous is always their which may reflect your other personality for example you may solve that questions @ home but fail to do so on interveiw..
So whats its solution..???
I think what the interveiwer wants is to make you on more & more stress so that he may test your stress dealing capacity..
he wanna test weather you are able to work under stressed condition or not..??
So this article states that logical tests are good.
I know that Microsoft uses these during their interview questions.
So if logical tests weed out the bad candidates from the good, Microsoft should have nothing but top-notch people right?
Then how is it that they keep getting nailed by glaringly obvious security holes in their software? How is it that they are getting ready to launch Vista and likely get a large population of their users to move off their about-to-be-crippled OS? Top-notch people don’t make the kind of stupid mistakes we are seeing from Microsoft.
I think it is because the interviewer is falling back on some false assumption that the logical puzzle does anything to expose the desirability of one candidate from another. Perhaps the interviewer should instead be someone with in-depth, practical knowledge of the job for which they are interviewing the candidate.
Microsoft isn’t as strict with their questions as Google is.
i think using puzzle logic for an interview is not really the best way of test the Intelligent of candidate. the fact that candidate A can solve a problem at the expense of candidate B doesn’t mean that he is more intelligent than Candidate B.
but for me i love logical puzzle questions
Here’s what happens when it gets out of hand:
http://www.codeslate.com/2007/01/you-dont-bury-survivors.html
logic questions are useless in this realm. when you think about it any actual employee has time to think of a solution to anything in half a day or maybe a whole day or week! these questions are ridiculous and are really meant to intimidate a candidate and see how they survive the stress! nothing to do w/intelligence!
hi
Your ‘proof’ of optimality isn’t complete: you haven’t shown why a qit or quadrinary bit (obviously, I’m making this up to be consistent with the article) isn’t better than a trit. That is, why is log N (base 3) better than log N (base 4)?
(Hint: has to do with 3 being a prime number.)
I didn’t read all the post, which I find interesting, but one (from #27. Timothy D) did stick out proving the whole point of any interview questions, be it logic or not, and for any reason. Timothy proved to me that he would be a difficult employee to work with unless the job called for a pessimistic person bent on proving the opposite of anything. He gave us his reaction and response to a situation (the question). You can use his reaction and solution as a base to most anything else he’ll ever face. Which, is to prove you wrong and tell you that it’s a bad idea? You wouldn’t want him in a situation where an answer, no matter the question or situation, needs an answer fast. He would be too busy questioning the question or nit picking the details. This is not someone who would just come up with a solution or would do it after much pain in analyzing the question. ‘Why’ is his answer to everything. He would suffer severely from paralysis by analysis.
The final answer “measures” your intelligence. The path to the final answer “measures” your smarts.
BTW, I’m a Software Engineer specializing in the latest RIA technologies using many different languages adapted to OOP methods, working with a major national company. I don’t know much and I suck at trivia, but put a computer in front of me with Interent access and I become lethal.
Thank you very much for this post. Many companies ask a puzzle-type questions to test the ability for logical thinking. As you know, programing i snot that big problem, but finding the best algorithm for a given problem is the main issue. I found http://www.technical-interview.com which has many puzzle interview questions
These kinds of questions are good if they are part of a larger interview since they test thinking skills, but the risk you run is that the interviewee already knows the solution. Admittedly, odds of that are low but a few friends and I interviewed for the same job once and after comparing notes we discovered that we were all asked the same puzzle question (“Why are manhole covers round?”) If you are going to go this route, be sure to have a good mix of questions of similar complexity (which in itself can be difficult) and ask different questions to each applicant in case they get a chance to talk to each other.
Employers lately complain that few candidates research their company before applying, before going to the interview, that the least they could do is take a good look at their Web site.
When I’ve asked candidates if they study a company beforehand, quite a few have explained, “Why bother? I don’t do that any more. I really want to talk about the job, and all they do is throw puzzles at me.”
Why not just throw a Rubik’s cube in front of the person and see the reaction?
It all depends on the what you are trying to measure.
When (yes many years ago) I was in comp sci you always had the majority of people copy your code, correct? Because if either you told them to screw off and solve the problem themselves or you just gave it to them. I thought why not give it to them that way when I am up for a job against this dolt people will be able to tell this guy / girl cant think their way out of a paper bag no matter how much rope and matches you give them.
People are lazy they don’t want to think. Programming exposes this more violently than any other profession I know. You ever notice the kind of programmers that can’t make saleable code . They are the ones that can’t think about how there code affects a system (tier database etc).
I have always found the people that I want to hire for technology are the ones that never like the answer given to them.
I like to ask them questions like this: Why does this application perform worse the more processors I add? There is no correct answer I listen to how they think.
hi can anyone help in finding some good book for such interview called the logical interview please..
i have an interview on tuesday thanks in advace..
I’m curious as to how many of the logic question friendly HR managers were asked logic questions themselves, and how well they performed.
I buckle up when asked anything mathematical. I’m the furthest thing from a mathematical mind, doesn’t run in my family. If you want me to quote literature, write you a screen play, or any other diction, I’ll be more than happy to.
I hadn’t experienced logic questions until an interview roughly a year ago, and it shocked me. It was actually the very first question the person asked me, and it was the first time I had ever been asked such a question.
Now I’ve had several interviews since this point, some of which have had them some of which have not.
This is a ridiculously intimidating thing to some people. I’m an EXTREMELY confident being, and I will ALWAYS research, research, test, research, test, research, test before I will give someone an incorrect answer to any question, regardless of how simply it is.
I work in Network Engineering/Project Management, I feel that taking a step back and giving yourself a fair amount of time to look at the big picture and build your solutions from this point is the best course of action, not having a client ask for a proposal and jotting down a list or an answer onto a napkin and handing it over.
In my business, one incorrect answer can cause millions of dollars lost, with SLAs, and hosted services, and whatever else you could surmise – spouting off quick, shortly deduced answers as opposed to mind mapping and design is a horrible idea.
wew i love you hehehehehhe…
Its a good post, i like the idea or view that, it is not the right answer that is sought during the logical questions, but the reasoning behind it…..There are times i thought it was the correct answer/answers which were sought
Great review, that made for nice reading, thanx
2 Uzair: I think you simply got a wrong idea why is it 3. It is base 3 simply because that is on how much information the scales provide you — either left selection is heavier, or right, or none (ie whatever was left behind the scales). Since any of those 3 outcomes is equiprobable (we have no cue where the heavy one is) we have to split all coins into 3 parts and that is why here is base 3.
if our scales could scale 3 items and show which one is heavier, than for optimal strategy we had to split 4 times, thus it would had been log base 4, which is not a prime number 😉
would like to ask a question…
when u take any five digit number and multiply by 2 will get the transpose of that number what can be the 5 digit number??
As a psychometrician, I can tell you that relying on any one question, no matter how good it is, is never a good idea. You are essentially overgeneralizing from a microsample of behavior. Standardized tests contain many items because many items are necessary for a reliable test.. A test’s validity coefficient (correlation with a criterion measure) can NEVER be higher than its reliability. This is the main problem with using measures like essays and interviews. Subjective scoring combined with the limited number of stimulus conditions produce very low reliabilities.
Forget logic puzzles; general intelligence is by far the best predictor of performance on any job, and the more complex the job the better it will predict (Schmidt & Hunter, 2004). If you seriously want to predict performance, use (1) a good intelligence test (the Wonderlic Personnel test for example) combined with (2) an extensive domain knowledge (list of specific stuff you want your employees to know) and (3) a situational judgment test (which you have already validated using your top employees). Modify the weighting of these scores as data accrues on the performance of new hires. Use interviews simply for determining who you would like to work with on a personal level or who would fit in with your company’s culture. An overreliance on interviews will cause you to focus on trivial, easily correctable traits in your candidates.
Schmidt F. L., & Hunter J. E.(2004). General Mental Ability in the World of Work: Occupational Attainment and Job Performance. Journal of Personality and Social Psychology, 86, 162-173.
logical puzzle questions just makes everything more fun
very interesting, but I don’t agree with you
Idetrorce
Just checking threads that I’ve commented on and noticed that Idetrorce said the same thing on nearly every thread I can find.
that’s some wicked spamming!
ujashdfu
[…] Imran On Tech claims that this question is used by Microsoft, Google and Amazon when they interview perspective employers. It’s seems a lot more logical and I would not be as intimidated by this question as I would be by the three stated above. […]
IF microsoft, goodle and amazon hire based on such questions, i’m surprised. Sure logical reasoning is an essential part of any computing job. But that does not start and end with that. Rather, they should be able to gauge if the candidate is “generally” intelligent, and will be able to come up with a solution in whichever way he wants. Unless actually implemented, no solution can be beforehand known to be optimal
I do agree with ppl and in this regard I found a good blog which will be helpful in handling tough interview questions like this.
http://placementsindia.blogspot.com
Interesting very interesting. It is one of the best post I found, My ideas are clear.
Thanks!
What a great post you made, Please update me by providing such sort of things. I need it so much, as I am MBA student from India. I faced some interviews, at that time I really got very scared. I am confident girl but interviewer made me confused how I dont know, but I failed in my last interview and that was my management interview . I dont want to face again that embarrassed moment in my life. Please tell me more things about job interviews. I am waiting for your reply.
Thanks!
Tanuja
to see how others think there way that thay think thay can see in it there limit and there amagin and there logical mind how it work
nice discussion.. i really appreciate it.
thanks,
saumya.
This is nonsense. All logic puzzles show is that the interviewer is too lazy or too inept at conversation to do a proper interview.
It’s realy helpfull for all those who like to test the logical aspect of candidate.
Cool post, it is important to test the logical and analytical skill of the candidate. See more digitalpbk.com/interview-questions
Thanks for the post http://www.technical-interview.com has many puzzle interview questions
Yeah I agree with Matt S…. I had exactly this question in an interview at JP Morgan. During the interview I was really happy to find the optimal solution in less than two minutes, but when I discussed afterwards with the other candidates I realized that I was the only one that didn’t know all these questions in advance. In fact, I m pretty sure that although I am the only one that actually solved the problem, I probably looked like the dumpest while spending two minutes instead of 30 secondes….
Perhaps the interviewer picked up on some clues that your brain was actually working to solve the problem while the others were faking it and/or just reciting the answer.
As a beginning programmer, I can see more value in these types of logic questions in an interview than “describe a time you did x or y” as such tall tales are not verifiable and can be embellished rather easily by the interviewee.
For those who are great at solving logic problem, how did you develop that part of your brain. Think back to the time when you first get started. Even with solutions provided, it can be challenging for some folks.
though i really appreciate the whole logical conversation….but i don’t think it would too much benificial for those who could’t analyse the whole text over the logicalogy… plz be precise and to the point…
You want them to be precise so it’s easier for you to follow?
Then why don’t you capitalize, punctuate, and spell normally so it’s easier for them to read?
You have provided a theoretical argument attempting to prove a solution to a practical problem (selecting the most suitable candidates) and yet you provide not one shred of EMPIRICAL evidence to support your hypothesis. I think perhaps that too many computer programmers confuse logic with reality. You give a logical explanation as to why logical problems work, but logic is always based on assumptions. Where are you statistics based on trials with control groups demonstrating that the method of posing such logic problems actually does select the best candidates? Your theory so far remains no more valid than stuff and nonsense.
Its a different story when someone completes a task on paper because that just tells you they can’t reason like a programmer does. although, i really dont think that a person should be judged just on solving a puzzle, when the programmer doesnt have any type of background on how to evaluate a person.
thank u man
I hate logic tests. I recently had one for a “Software Support” opening of all things (no programming – just support at a small company [less than 20 people!]) and I was put into a room with 5 other candidates (none of us knew we were “interviewing” at the same time).
Anyways, we were all given 50 questions and 10 minutes to complete as many questions as possible. You weren’t marked down if you skipped a question, but you lost a point if you answered something incorrectly. So theoretically, if you answered 25 questions right and got 25 wrong, your score would be zero.
Problem was, you only had 10 minutes and the test was a mix of math, pattern, visual and word brain teasers. I tried doing all of them in a row, not skipping anything (I thought that would show I wasn’t looking for only the easy questions).
At the end of 10 minutes I felt confident in my 21 or so questions I answered, having only skipped one. I was told I wouldn’t be brought in for a 2nd interview (the real face to face interview) because I only scored 18. A 20 was needed to get to the next interview. 😡
So me answering questions correctly every 33.333 seconds was not good enough to do phone/email support…but if I could have answered one every 30 seconds, I was worth their time.
Screw that.
Probably better off anyhow – the software to be supported was banking software written in COBOL over 25 years ago.
hi
Nothing you say will convince me. A test can only measure what its questions measure. So-called ‘logical puzzles’ only measure one or a few specific types of logic, and all of the same certain flavour it seems. Some people do these puzzles for fun but are not computer programmers but will have an advantage due to familiarity. As an educational expert, my experience tells me that a test can only measure as much as it measures. Sometimes it measures less, as some people react negatively to such tests, but it never measures more. If you want to really assess logical thinking, and its various sub-skills, then you have to employ a good psychologist to administer a well tried and tested measure (though never infallible) to get a fairly robust measure. The amateurish tests given by IT companies seem to lack robustness to me. Also, they assess a person’s motivation when put on the spot in an unfamiliar setting. You may think this is important, but I wager the specific scenario given is rarely(!) if ever going to arise in the work place (unles you are writing software for Mensa). To recruit the most suitable candidates you need the most suitable test – to recruit a computer programmer, get them programming a computer! Personally, I get turned-off by companies who recruit by these methods as they come across as rather ‘academic’, air-headed and theoretic and lacking in pragmatism. Computer programming does have a theoretic beauty in its own right, which I am sure we all appreciate, but for me there has to be some connection to reality for me to be engaged.
I was interviewing for a sales position – for online advertising. After 2 hours of back and forth questions with the sales manager and an associate, the marketing director came in and after 15 minutes of the same questions asked from me, he stated “Okay now, I will give you a math question and a logic one, you fail you don’t continue on. Ready to begin?”
Now remind you this is a sales position I am interviewing for.
Q1 – if you have CPC for $.10 and 34,500 CPM, and out of those 4560 clicks, and from those clicks you have 250 users.
What is the CPA? (please complete problem with a pen and scratch paper)
With the director sitting next to me and watching my note taking and scribbling numbers down, and now being completely frazzled – I couldn’t do simple multiplication or division – I was then asked, “you can do math, right?”
As you can see this was not going well…..
Q2 – The above quarter question, but worded that you can’t weigh them in your hand, or tell by looking at them which quarter weighs more. You can only weigh them twice on the scale.
I immediately said split them 4/4 then 2/2 but of course that was wrong. But after a few minutes of the director staring at me and saying No that s wrong, wrong wrong and then said if this is going to take long then let me know or do you give up – I finally said yes I give up and what is the answer.
After I was informed of the answer he immediately said that HR will let me know if I made it to the next round of interviews and walked out.
I am going to say I did not get this job.
Onto flipping burgers I guess!
Such a test is clearly not about selecting someone with maths or logic skills, but selecting someone who is aggressive and over-confident whilst at the same time easy to manipulate. Such recruiters are honestly not worth working for.
As more consolation for you, I have a first class degree in science and maths from an outstanding university and I have excellent problem-solving skills, but I would not have been able to do a simple sum in that kind of hostile environment. My only instinct would have been to tell them where to shove their stupid job! What has such a test to do with the way most people work in the real world? Perhaps that was the purpose of the test, to see if you work well whilst being harassed, in which case not getting the job is likely a blessing in disguise. Sadly, too many employers are of a similar perverted mindset to those you describe. This is incompetence on the part of the interviewers, and no doubt they join the ranks moaning about the lack of candidates who can do basic sums!
Excellent article. We should also be talking about the lunacy behind the use of credit scores to pre-judge discipline from non-discipline candidates. But on logical question. I cautiously support their use.
I have taught college level for over 12 years, and worked in the real world for over 14. I also have a psychology academic background, so am familiar with the world of theoretical and practical thoughts processes. Your well thought out and on the mark response is one of the most profound and legitimate ones. Especially on the notion that an interviewer with unknown background in relevant science can be assumed to have such credibility to be accurate in their assessment. My experiences in the real world prove 90% of all this support for logical questions to be full of more gobbledygook then anything else. I totally agree with you that like every job interview, watching the person ar work for a few days after being hire will unscramble the theory from reality. Fact is that I have seen some of my best employees turn out to have been the lesser impressive ones on interviews. Why? Because in many cases these questions ignore the abilitity of some people to excel in real world problem solving versus academic test games. This reminds me of the fallacies behind the use of credit scores to determine the most responsible workers. What a joke. I had this one lady with horrible credit scores, who was so effective..that she became my right hand person on the team. Fact is there are too many unknowns for an interviewer to give too much weight to these questions. That lady had bad credit because her husband embezzled her financials, impacting her credit. I saw pass her credit score by engaging her in real life scenarios of our business and I was amazed at her abilities to think through valuable solutions. Things these logical questions fail to pick up. I am not totally against logic questions. I am against how they are being loosely used by wanna-be psychologist interviewers.
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This is a pretty basic question in my opinion. You can apply elimination process to solve it.
“Split 8 coins into 2 parts (4 on each scale)
set aside the group with lesser weight,
Split the remaining 4 coins into 2 groups (2 coins on each scale) and set aside the group with lesser weight.
Now weigh the remaining 2 coins against each other to find out which one is the heavier coin.
You only have to use the scale 3 times to find the heavier coin. 🙂
He
Here’s a logic puzzle to pose to the condescending techie interviewer when you’re forced to respond to one of these irrelevant logic tests:
You have four candidates that you’ve interviewed to be a software developer reporting to you. The first candidate is an Asian female, the second is a white male, the third is a black female, and the fourth is a gay Hispanic male. You have to make a decision to hire of them by tomorrow. All candidates are equally qualified. Who are you going to offer the job to and why?
As with the logic puzzle, this question is designed to un-nerve the interviewer, and any response could be construed as the wrong answer. For example, if the arrogant techno-dickwad trying to trip you up with the logical puzzle is a white male, and he answers “I would hire the white male”, your comment could be “so I see that you’re only comfortable with hiring someone who looks like you”. Or, if he responds that “the Asian female”, your comment could be “so I see that you’re buying into the stereotype that Asian people are inherently smarter than white, black, and Hispanic people.” And so on. If he asks “how would I know the Hispanic male is gay?”, your response could be “because he made it a point to inform you during the interview just to see your reaction”.
The trouble is the best creativity does not come out of the most creative people when they are put on the spot. If you want creative problem solvers then give them a real problem and a week to solve it. If you want people who can find solutions on the spot then you probably don’t need someone who is especially creative in the first place (i.e. the problems you deal with are likely quite bite-sized and actually not that difficult).
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Hello! These are just voodoo hiring practices. Other people ask these questions so they feel like they are supposed to. They know that not answering the question is “bad” and answering is “good”, but they can’t tell you why beyond non-answers like “a developer needs these skills”. They are a waste of time and an indicator that the interviewer is not a competent interviewer. By the way the best paper writing service that I saw: http://speedypaper.net/
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How about actually gaining an understanding of what the job entails and reading the candidate’s resume. The truth is that most offshore tech recruiters and the hiring manager has a clue about what the task involves. Thats why you have to resort to these silly and irrelevant vetting tests.
How about actually gaining an understanding of what the job entails and reading the candidate’s resume. The truth is that most offshore tech recruiters and the hiring manager don’t have a clue about what the task involves. Thats why you have to resort to these silly and irrelevant vetting tests.