Created 10th September, 2009 07:48 (UTC), last edited 10th September, 2009 08:14 (UTC)

Birthday paradox

Because it seems to be birthday season around me at the moment, another birthday puzzle.

I'm sure pretty much everybody already knows about the *Birthday Paradox*. The birthday paradox is that you need surprisingly few friends to have two that share a birthday.

**How many friends do you need for a 50% chance that two share the same birthday? How many for a 90% chance?**

Let's say I know 150 people through the South East Asian BarCamps. **If I only know that 2 of them share a birthday what does that tell me about how many of their birthdays I know.**

Categories: BeerCamp puzzle

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