Insight · ★★★☆☆ · ~6 min
The Birthday Paradox
How few people in a room until two share a birthday, more likely than not?
by MindYourPuzzle
A probability result so counter-intuitive it's called a "paradox," even though it's just arithmetic.
People walk into a room one by one. We want the moment when it becomes more likely than not that at least two of them share the same birthday (same day and month; ignore leap years, assume birthdays are uniformly spread across 365 days).
Most people guess you'd need somewhere near 183 (half of 365).
What is the smallest number of people for which the probability of a shared birthday exceeds 50%?
(Answer with the number of people.)
people
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