Candidates in an exam 443 candidates enter the exam hall. There are 20 rows of seats I'm the hall. Each row has 25 seats. At least how many rows have an equal number of candidates.
My attempt
Seat 25 in the first row  24 in the second and so on...but I cannot find the worst case scenario.

We have to distribute $500-443=57$ balls into $20$ containers such that the contents of the containers are as different as possible. Having two containers each with $0$, $1$, $\ldots$, $9$ balls requires $90$ balls. Therefore it is impossible to do it with no three containers getting an equal number of balls.
We now try it with three containers each getting $0$, $1$, $\ldots$ balls. It turns out that we need $3(0+1+\ldots+5)=45$ balls to serve $18$ of the $20$ containers, and that there are just $2\cdot 6$ balls left to  put into the last two containers.
