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Why a small ball on a big ball shoots up nine times higher: the two-step bounce
Drop a tennis ball on top of a basketball and the small ball can fly far above the height it fell from. Nothing is cheating: it is a two-step bounce. The floor…
Why 23 people are enough for a shared birthday: counting pairs, not people
Put 23 people in a room and the chance that two share a birthday is already 51%. It feels far too low a number, because we picture one person matching our…