Mathematics
The Birthday Paradox: Probability in a Shared Calendar
Quick fact
With only 23 people, the probability of a shared birthday is about 50.73% — and with 70 people, it jumps to over 99.9%.
Why this is interesting
If you’re in a room with just 22 other people, there’s a greater than 50% chance that at least two of you share a birthday. How can that be?