Hacker News Reader

I knew an engineer who used the 'why are manhole covers round' question in every interview. He was always shocked at how 'quickly' the interviewee figured out the 'answer' of "so it doesn't fall down the hole". These new kids - they're smart. As far as I know, he never figured out that 90% of people have already heard that one.

View on HN

My answer to the question was that a covers follow the shape of the hole underneath; the hole underneath is round because they are generally cut with rotating tools that create a circular shape. Cutting square holes is more expensive.

pffft, what a silly question. Manhole covers are round because manholes are round...why would you make a square cover for a round hole?

(Seriously though there's a lot of conceivable reasons, and while that's one I doubt it's a major one, a lip prevents it. I think the fact that a circle doesn't need to be "lined up" and that they are easier to move, etc are much more important)

Reply on news.ycombinator.com