Math & Logic · Ages 18+
Riddle #210
Twenty-three people are picked at random and put in one room. Roughly what is the probability that at least two of them share a birthday?
You solved this one before
Answer: About 50% — 50.7%, to be exact
What matters is not "you against everyone else" but the 253 possible pairs among 23 people. Multiplying 365/365 × 364/365 × … × 343/365 gives about a 49.3% chance of no shared birthday at all.