Riddles and Quiz in Interviews

by Krishna on December 8, 2007

Try solving the puzzle below. The answer and an explanation of how to solve the generic version of the problem can be found in this article by Jack Wert.

You have 9 coins, one of which is heavier than the rest. You are provided a weighing scale. What is the least number of weighings required to discover the heavier coin?

You may have already known the answer. Or you may not, but after deriving the answer or looking it up, you will feel confident to answer any similar question in future. Someone asking you this puzzle again cannot say whether you knew the answer or found it yourself, unless you tell them.

This is my primary objection against those people and companies who try to filter potential employees by asking them to solve puzzles and problems during interviews. It is impossible to understand if someone is intelligent through such methods, because these puzzles can be learnt.

Once you understand the basic technique for solving the problem, you can handle many similar problems too. And I am not just talking about above-average people. Most people can understand techniques and remember things, especially if doing that would lead to benefits like a job.

Another interviewing error is to convert the interview session into some sort of quiz contest. The interviewer asks obscure details about a particular technology, perhaps under the misguided notion that everyone in the world works in the exact same environment as he does. Many of these questions can be easily looked up through the API documentation, a Google search, or some book.

Such interviews are a waste of time even if you have a lot of time. The reason is that they measure the wrong things:

  1. What you can discover is more important than what you can remember. There are more things that you can discover than you can remember. And there are only so many things you can remember because you are a human being and do NOT have a RAID array.
  2. Your ability to learn is more important than your current knowledge. Today’s innovation continues to make a mockery of what you have learnt yesterday. Especially in the software industry. If you were an expert 3 years ago and you learnt nothing new since, you are a dodo today.
  3. The big picture is more important than the small details. The latter is not a percentage game. Out of the thousands of technical idiosyncrasies and code snippets that you have accumulated, you may use only a handful ever again. Worse, you may not even remember that you had saved the information and now have to look it up. Focus on the big picture. Get help when you need to know more detail. That is what the Internet is for.
  4. The team is more important than the individual: The individual’s ability to contribute to the team and work in a particular role is more vital to its success than the individual’s capability. Effective communication, mutual respect, and common goals drive success, not a bunch of talented individuals thrown together in a room.

When you interview, try to understand the “fit” of the individual with your team. Is he a person who can change and grow? Is he interested in learning and self-improvement? Is he interested in the same technical things you are? Does he have the same values as you do? Is he motivated by the same things that you are?

Don’t be in too much of a hurry to hire someone who has only passed your technical qualifications. If they don’t blend in your environment, all they provide you is temporary relief for a vacant position. In the long run, their inability to grow and adjust will come to haunt you.

P.S. This article is meant for interviewers. If you are an interviewee, don’t try to beat the system. Pick up a few puzzle books and learn the answers. Read the commonly asked questions in your industry and be prepared before going for the interview. I don’t know why more people don’t do this.


Kalpesh December 9, 2007 at 7:03 am


IMO, Puzzle type questions are open-ended questions (unless both interviewer & interviewee are fixed on answers). It pushes the people to think & enter into a discussion mode.

Good to check, how people can apply their creativity?

I agree to most points (1 to 4) that you have raised. If I am working on the usual stuff, I might not need what Hanselman knows. However, Hanselman questions shows that one went to examine things under the hood to see how they work (one might not use all of it. but, one is aware of such a thing).

I could use all that comes out of vendor factory (MS in case of asp.net) & be happy with it. Alternatively, I could be thinking & designing things in a better way, use open source solutions and learn some better way of doing things (e.g. MVC)

There is no doubt, that humane skills are equally (or more) important. And interview is not just about tech skills. One interacts with other person to see how they talk, behave, argue or work in a hypothetical situation etc.

I disagree with your view of looking up techinterviews.com. Well, it can help for the time being - but the nature & age of /SW industry makes us learning constantly (albeit too much as of now).

Who would you like more? The person, who would look at sites & answer you OR use skills/time to learn things & apply ingenuity to things?

You are an example of things such as your reading list 🙂 - shows that one don't just read things for the sake of it.

I typed in too much 🙂

Krishna Kumar December 9, 2007 at 7:51 am

Kalpesh, I should clarify: Sometimes a technical person may be really good, but he may have specialized in some other area, or does not bother to remember details that can be easily looked up. This may cause problems during the interview.

Also, I would definitely prefer someone who can use their skills and time. So looking up techinterviews is meant for interviewees. Interviewers should take care not to ask questions that someone can easily look up.

Kalpesh December 9, 2007 at 10:29 pm


What is the point of "remembering" things which can be looked up? In one of the interview, I was asked - what are the methods on this specific class?

One should not expect any person to remember the documentation. It is more about awareness of framework, concepts & intelligent way of applying things.

More so, when you say "Interviewers should take care not to ask questions that someone can easily look up" - how does it help to interviewee looking up things?

I am confused about what you wish to say. Please help me understand.

Krishna Kumar December 10, 2007 at 4:15 am

Kalpesh, there are 2 roles you can play. If you are interviewing a candidate for a job in your company, you can conduct the right kind of interview. You can ask them the right kind of technical questions. You can also measure their fit with respect to the team. You can avoid asking questions for answers that are obscure or can be easily looked up.

But when you are on the other side (you are the candidate being interviewed), you have no control over what the interviewer may ask you. You cannot demand that the interviewer ask you only the right technical questions. It is in your best interest to learn details that may be asked. You may think that the interviewer is unfair or incompetent, but if you need the job, you have to play by their rules.

avenuez December 23, 2007 at 7:39 am

When I read this post, I felt a twang of guilt. I've been on the receiving end of these types of questions during an interview, and I've been familiar with the types of answers they expect. So I had an advantage, not because I was clever on the spot, but because I had already played the game.

I like your reasons why these questions don't work.

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