How many people must be in a room for a better than 50% chance that two share a birthday?

How close can you get? Make your own guess and earn points before you look at the answer.

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Show the answer and the reasoning

The answer

23 people

Only 23. With 23 people there are 253 pairs, and that is enough.

How to get there

1. Not you against everyone, but everyone against everyone
2. 23 people form 253 pairs, which gives 50.7%

Source: Birthday paradox

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