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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?