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[–] 1 point 8 months ago* (last edited 8 months ago) (2 children)

I think the question is usually frames as "how many people does it take to make it at least 50% likely that two people will share a birthday", or more likely than not etc.

A guarantee would need 366 people. But most people are satisfied with "more likely than not", "90% chance", or "99% chance".

EDIT: I meant 367, not 366!

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  • [+] -8 points 8 months ago (3 children)

    366 would not guarantee it. That's not how probability works. You cannot guarantee a shared birthday without selecting people. And not to mention, birthdays aren't evenly distributed.

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  • [–] 3 points 8 months ago (2 children)

    Once you have more people than days in a year it's not about statistics anymore

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  • [–] 8 points 8 months ago (1 child)

    366 people wouldnt guarantee no shared birthdays though. There could still be one leap year baby in that bunch. But what are the odds in that?

    2.6 • 10^-158 , if anyone is curious.

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