I call these interview questions "Smart" or "Problem Solving" questions. While it seems like a silly question to be asking in a job interview, this style of questioning is growing in popularity among professional interviewers.
Popularized by Microsoft, the "Smart" or "Problem Solving" question is designed give the interviewer a sample of your mental horsepower, ability to think on your feet, and flexibility and creativity.
You are not supposed to actually know the answer. The interview question is to see if you can come up with a credible answer and back that answer up with some kind of logic, calculation, or reasoned analysis.
Don’t throw your hands up in frustration and whine, "I don’t know!" You will be judged as inflexible and easily frustrated by out-of-the-box ideas. You don’t want to give that impression in a job interview situation.
Do act intrigued by the question (even if you’re not). Show that you are willing to engage in an off-beat exercise. Have some fun with it. Relax.
Do puzzle your way to an answer, even if you know it’s probably wrong. Think out loud. Let the interviewer know how you are going to try to get to your best answer.
Do ask clarifying questions of the interviewer if you need more information to get to the answer. Interviewers like to see some give and take during these questions.
Don’t get carried away and ask too many detailed questions that delay the interview. It’s not important to be right. You just have to come up with a credible answer that you can back up with a credible analysis of some kind. It is possible to be too detail oriented and lose sight of the goal of the question. Don't fall into this trap.
Do feel comfortable making assumptions, but be careful to state them to the interviewer.
If these kinds of questions are difficult for you, buy yourself a mental exercise puzzle book and practice-practice-practice until you become more comfortable. You can try making up your own questions, or have a friend make up a few, and go to town on them.
Case interviews are more in-depth, but are very similar. Practice case interviews would seriously help you answer these questions also. Consider Vault's Guide to the Case Interview
as a resource I can confidently recommend.
Sample Answer:
"Hmmm… Wow. Interesting question. Well, I suppose there might be several reasons for that. I’m not sure I know the true answer, but let me take some educated guesses.
"They might be round because they are heavy. It would be easier for one person to lift and roll around. If they were square, you couldn’t roll them, and it would take two to lift one.
"Maybe they are round because they are expensive to make, and a round cover would use less materials than a square cover because the volume of a circle is less than a square.
"They might also be round for safety reasons. Maybe the corners could warp and come up into the street and punch holes in tires over time.
Not sure I got it, but those are at least a few ideas on why they might be round."
