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