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Interview Brain Teasers Medium 2 min

Why are manhole covers usually round rather than square?

Hint
Think about whether a round cover can fall through its own opening.

Answer

A circular cover cannot fall through a circular opening of the same diameter, regardless of how it is rotated.

Explanation

A square cover can potentially fall diagonally through a square opening. A round cover has constant width, so it cannot pass through its matching opening.

Step-by-Step Solution

A circle has the same width in every direction.
Therefore it cannot fall through an opening smaller than its diameter.
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