Lateral Thinking · Ages 18+
Riddle #228
Manhole covers are round almost everywhere in the world. There is one practical reason squares, rectangles, and triangles all fail on. What is it?
You solved this one before
Open-ended riddle: think it through, then reveal the answer.
Answer: A round cover cannot fall through its own hole. A square one, turned on its diagonal, drops straight down the shaft onto whoever is working below.
A circle has the same width in every direction; a square's diagonal is about 1.41 times its side, so it fits through the opening it just covered.