Random and seemingly strange job interview questions are the subject of countless articles during hiring season. Most of these are not about reaching a right answer, but rather to see how someone’s brain works in reaching towards an answer. 

Microsoft used questions like this to ‘distinguish between people who are smart and get things done, people who are smart but don’t get things done, and people who get things done but are not smart.’ Have you thought of any reasons yet? Here’s a few options: 

• A round manhole cover cannot fall through its circular opening, whereas a square manhole cover could fall in if it were inserted diagonally in the hole.
• Circular covers don’t need to be rotated or precisely aligned when placing them on the opening.
• A round manhole cover is easily moved and rolled.
• Human beings have a roughly circular cross-section.
• Round tubes are the strongest shape against the compression of the earth around them, so the cover of the tube would naturally be round as well.
• It’s easier to dig a circular hole.
• Round castings are much easier to manufacture using a lathe.

(Source)