Twenty-three people in a room and the odds of a shared birthday cross fifty percent. I explained this at my own party, out loud, with a whiteboard. Attendance next year is projected lower.
P(shared) = 1 - 365!/(365^23 · 342!) ≈ 0.507The paradox is not that the number is 23. The paradox is thinking anyone wants to hear about it near a cake.
