I'm stuck with the following question which is taken from SAT-like exam:
How many $ 5 \times 5 $ ceramic tiles are needed to cover rectangular area whose size is $ 10^4 $ units squared (you can't cut the tiles).
The answer that I've got is $400$ (${10^4} \over {5*5}$), however, it is wrong. I don't understand where's the problem. I would appreciate any help.