Puzzles
The shared birthday bet
How many people do you need in a room before it's more likely than not that two of them share a birthday?
Reveal the answer
Just 23. With 23 people there are 253 possible pairs, and the odds of at least one match pass 50%. By 70 people it's 99.9%. Intuition fails because you instinctively compare everyone to yourself, not everyone to everyone.