An

old chestnut goes like this:

How many people do you need to have together for the
probability that two of them have the same birthday to be at least 50%?

Usually these simplifying assumptions are used:

This is also written up in

Birthday paradox **(Warning: partial spoiler in link)** but it's not really a

paradox and the calculation is not described over there, only the answer, so I'm not using that node for this

puzzle.

Answer