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The Birthday Problem


Question:

You are at a party with 22 other people. What is more likely - that no two people have the same birth date (day and month) or that at least two people do have the same birth date?


Answer:

This is called The Birthday Problem. Among 23 random people, the chance that two have the same birth date is 50.7%. Most people intuitively think that since there are 365 days in a year, the 50% threshold wouldn’t occur until around 182 or so.


Source: Wikipedia - The BIrthday Problem