Lost_My_MindBallpitts are never washed. Not even once. However, some kids pee in there. This means there is a 100% chance that all balls in ballpits have been peed on, and not washed at some point.
You’d be better off claiming that there’s a 100% chance that at least 1 ball has urine on it assuming that 100% of all ball pits have at least one urine incident.