We’ve called this article “Interview Questions that Make You Think Out Loud,” but it might just as well be called “Interview Questions that Make You Squirm.” These are the questions interviewers use to get inside your head, to see how well you can solve problems. They’re also the questions you didn’t count on, because you won’t read about them in most books.

Be open-minded

You’ve probably heard of the famous question, “Why are manhole covers round?” My friend Nick once shocked an interviewer by giving the “correct” answer: Because a circular top is the only shape that won’t fall into the hole no matter how it’s oriented. But most interviewers aren’t looking for a “correct” answer. In fact, Nick advises (hindsight is 20/20!), “My best non-answer advice is not to think there is only one answer-be open-minded.”

Creative thinking, problem solving
What the interviewer really wants to know is, “Are you creative? Can you problem-solve? Can you think on your feet?” But if he asks you that, of course you’re going to say yes. So he’s trying to force you to do the work in front of him, out loud, so he can evaluate you for himself.

A good answer
If he asks you the manhole question, you might answer him by saying, “Well, I’m not sure, but I’ve got a couple of guesses:

  • Because a circular top is the only shape that won’t fall into the hole no matter how it’s oriented;
  • Because manhole covers are actually much heavier than they look, and when repairmen remove them, it’s easiest if they can roll them around on their edges;
  • Because round is the most aesthetically pleasing shape;
  • Because repairmen are less likely to hurt themselves on sharp edges or corners;
  • Because the round edges won’t slice through wires or other delicate assemblies.”

Why this works

You’ve just shown him that you can look at a problem from multiple angles and that you can generate ideas quickly under pressure.

Phone booths in New York City
Some problem solving questions sound like number questions, but they’re just like the manhole cover question underneath:

Interviewer: How many phone booths are there in New York City?
You: Well…I could try calling the major phone booth distributors and asking how many phone booths they’ve got out there. Or I could estimate: to figure this one out, it would help me to have a map of New York City…I’d estimate that there’s a phone booth every block on a major avenue…maybe only one every other block on the cross streets…and obviously I’d want to subtract for the area of Central Park….

Why this works
You’ve broken the problem down, suggested one pretty quick way to solve it, then shown how you’d do research if you had to work it out by yourself. You’ve also shown what factors you take into account when you’re solving problems.

Practice makes perfect
The best way to get good at answering questions like these is to practice answering as many as possible. Many sites on the web offer brain teaser questions (just search on “brain teasers”). GRE and GMAT preparation books and courses also often focus on logic and problem-solving questions and techniques for answering them.

Other questions we like:

  • How many gas stations are there in the U.S.?
  • What is the square footage of Mexico?
  • How many tubes of toothpaste are manufactured in the U.S. every year?
  • How many bricks in the Empire State Building? (Beware trick questions! If you find you’ve answered, in all earnestness, a trick question, make sure you laugh at yourself!)

We leave you with this:

In your cellar there are three light switches that are in the OFF position. Each switch controls 1 of 3 light bulbs on the floor above. You may move any of switches but you may only go upstairs to inspect the bulbs one at a time. How can you determine the switch for each bulb with one inspection?

Answer: Turn switch 1 on for 5 minutes, then turn it off. Turn switch 2 on and go inspect. The hot bulb is controlled by switch 1, the lit bulb is controlled by switch 2, and the unlit and cold bulb is controlled by switch 3.