Well I’ll tell you, but if all you want is the answer then you completely missed the point of the question.
“Why are manhole covers round?” is a now famous interview question considered anywhere from insightful and thought provoking to downright stupid by people on the receiving end.
Why do interviewers ask it?
Well, to be clear, it’s so well known these days that that they shouldn’t really be asking it anymore.
Originally the question was asked simply to see how interviewees responded.
The idea wasn’t to see what the candidate knew, but rather to get a sense for an interview candidate’s ability to think on his or her feet outside of their area of expertise.
The way a candidate approaches problems, thinks of and presents potential solutions, defends them or discards them are all exceptionally relevant to the interviewer.
It’s a simple question. There are simple answers. But the great not-so-secret about this question, and indeed these types of questions in general, that everyone seems to miss is that it’s not about the answer! The interviewer cares much more about how you arrive a whatever answer you get than
what that answer is.
Are you thinking logically? Is there method or madness to the solutions you consider, accept, and discard? Are you even willing to entertain such an absurd question?
If you’re now getting yourself all wrapped up about the answer, if you think there’s a right or wrong answer, then I say again: you’re missing the point! It’s not about the answer – it’s about how the candidate responds to the question.
Oh. You still want the answer.
Remember, there is no single or “correct” answer.
The most common answer is simply that a round manhole cover can’t fall into the hole it covers.
But I did tell you that there’s more than one answer. Heavy, round manhole covers are easier for one person to move by standing it on end and rolling. Also, you don’t have to “align” a manhole cover to it’s hole. Any orientation will do.
My late father, a mechanical engineer, claimed an answer I hadn’t heard before: that round manhole covers are easier to manufacture. That’s a nifty answer and it would have done great in the interview except he also claimed that was the only reason and all the others were wrong. Whoops.
And for the record, round is not the ONLY shape that can’t fall into its hole. There’s a class of such shapes referred to as “Reuleaux polygons“. The common characteristic is that they share a constant width or diameter.
But if you walk into an interview having simply memorized answers there’s a good chance you’ll fail miserably. What interviewers care about is that you know why, and how and much, much more.
Just knowing an answer isn’t enough.