Here's a fun brain teaser: How large does a random group of people have to be for there to be a 50% chance that at least two of the people will share a birthday? The answer is 23, which surprises many ...

How many people need to be in a room before there's a greater probability than chance that two of them share a birthday? Numberphile approaches the famous birthday paradox without a computer.

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How popular is your day of birth? Celebrate the rarest birthdays—and the most common!

The birthday paradox, a classic illustration used in probability theory, states the probability that in a set of randomly chosen people, a pair will have the same birthday. The magic number is 23, ...