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