Add balls forever, remove one each time — how many are left at infinity?
At each step, ten balls numbered consecutively are added to a vase and one ball is removed, always the lowest-numbered ball still inside. If this repeats infinitely many times in a compressed sequence of steps, how many balls remain in the vase at the end?
Reveal the answer
Zero — because ball number n is removed at step n, every single ball you can name eventually gets removed, so none remain at the "end" of the process, even though the vase's count grows without bound before then. The puzzle, formalized by mathematician John E. Littlewood, shows how badly intuition about infinite processes can mislead you when the answer depends on exactly how items are removed, not just how many.