Helping people with computers... one answer at a time.
Interviewing for technical positions can be tricky, but it can also be fun. Expect odd questions, and plan on being able to think on your feet.
So Just Why *Are* Manhole Covers Round?
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Well I'll tell you, but if all you want is the answer then you completely missed the point of the question.
And why am I talking about manhole covers anyway? Well, to be honest it's an excuse to plug my ebook of interviewing tips for both interviewees and interviewers: Nailing Your Interview, now available on Kindle. (And you don't even need a Kindle!)
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"Why are manhole covers round?" is a now famous interview question considered anywhere from thought provoking to downright stupid by people on the receiving end.
Why do interviewers ask it? Well, it's so well known now that they shouldn't anymore but originally it was to see how interviewees responded. It's a way 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 the candidate approaches the problem, thinks of and presents potential solutions, defends them, or discards them are all relevant to the interviewer.
It's a simple question. There are simple answers. But the great not-so-secret about these types of questions 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?
Oh. You still want the 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.
I interviewed hundreds of technical candidates in my years at Microsoft. If you're going to be interviewing for a job, Nailing Your Interview will give you some insights on what the interviewers are really looking for when they talk to you. If you're an interviewer, Nailing Your Interview will also give you tips to help you identify and hire that star candidate you're looking for.
Article C1846 - October 2, 2003 « »
Leo A. Notenboom has been playing with computers since he
was required to take a programming class in 1976. An 18 year career as a programmer at Microsoft soon followed.
After "retiring" in 2001, Leo started Ask Leo! in 2003 as a place for answers
to common computer and technical questions. More about Leo.
October 21, 2011 9:04 PM
Original manhole covers were made of wood core pieces of tree trunks: round, strong, cheap, abundant.
November 14, 2011 11:24 AM
What if I answer that Manhole Covers are round because "Manholes" are round...!!!! :p
January 11, 2012 7:56 AM
You will come across some tricky interview questions when it comes time to interview for a job. It may seem as though some job interview questions are designed to put you “on the spot.” To a certain extent they are.Peculiar and indiscriminate interview questions may not seem politically correct, but there is always an interviewer ready to throw one at you, and they expect an answer as well.
February 1, 2012 8:48 AM
because a square manhole cover won't fit
July 30, 2012 11:09 AM
The real question of course should be why manholes are round? The covers are obviously round to fit the manhole.