Editing BirthdayProblem
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COLUMN_START^ If you have two people in a room, the probability that they share a birthday is ~really, ~really small. On the other hand, once there are 400 people in a room it's absolutely certain that some two of them will share a birthday. So as you add people to the room, the probability of a shared birthday, /any/ shared birthday, goes from nearly zero right up to 1. * What is the smallest group size that would give a better that even chance of two people sharing the ~same birthday? For a group size of n, the probability that all people have a different Birthday = EQN:\frac{364}{365}\times\frac{363}{365}\times\frac{362}{365}...\frac{366-n}{365} = p The probability that at least one pair share a birthday = 1 - p If there are 23 or more (randomly chosen) people in a group then there is a more than even chance that two will share a birthday COLUMN_SPLIT^ | Number _ of People | Chance of _ no pairs | Chance of _ at least _ one pair | | 1 | 1 | 0 | | 2 | 0.997 | 0.003 | | 3 | 0.992 | 0.008 | | 4 | 0.984 | 0.016 | | . | ... | ... | | 22 | 0.524 | 0.476 | | 23 | 0.493 | 0.507 | COLUMN_END