In a room of 23 people, there's a 50% chance two share a birthday. With 70, it's 99.9%.
Why?
It's not 'someone shares MY birthday' — it's any pair. With 23 people, there are C(23,2) = 253 pairs. Lots of chances.
In a room of 23 people, there's a 50% chance two share a birthday. With 70, it's 99.9%.
It's not 'someone shares MY birthday' — it's any pair. With 23 people, there are C(23,2) = 253 pairs. Lots of chances.