While on some crazy hunt to find information about Random Number Generators on computers, I came across this page on Wikipedia about the Birthday Paradox.
Simply put, it’s the probability that two people in a room will share the same birthday. With just 23 people there’s a 50% probability that at least two of them will share a birthday.
I like to think about these puzzles in different ways to explain them to myself. I am usually fooled, like most people, when I first think about it (23 just seems sooo low…) Then I start to think about it more rationally… there’s a 22/365 chance that somebody has the same birthday as person A, and a 21/365 chance that somebody matches person B…and so on – they all add up (don’t quote me on the maths nor the theory…)
The other good one is the Monty Hall problem, which takes some explaining…
In fact – the helpful bods at Wikipedia have created a category of probability theory paradoxes – enjoy!