Mathematical
Ross-Littlewood Paradox
Adding and removing from an infinite set yields unclear results
Overview
A paradox about infinite processes involving adding and removing elements from a set.
At step n, add balls numbered 10n-9 to 10n, then remove ball n. After infinitely many steps, how many balls remain? Argument 1: You add 10 and remove 1 each time, so infinitely many remain. Argument 2: Every numbered ball is eventually removed, so zero remain.