ELi5: what’s the birthday paradox ? And is its mathematical basics a correct proof?
In: Mathematics
To start, it isn’t really a _paradox_, but rather a mathematical proof that seems counterintuitive until you understand it.
The birthday problem states that in a random group of 23 people, there is about a 50 percent chance that two people have the same birthday. That _seems_ wrong, because the chance of someone having any given birthday is 1/365.25 – so 23 people shouldn’t be able to get to 50%. You’d need more than that, right?!?
What people miss is that they don’t have to match any one specific birthday, but _any_ of the birthdays of the remaining 22 people. This dramatically chances the probability.
If you want a description of the exact math behind it, [this link is good](https://statisticsbyjim.com/fun/birthday-problem/)
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