Facebook Birthday Paradox
September 29th, 2008
I checked facebook today and noticed that none of my friends have birthdays on Sept 28,29, or 30. Being the nerd I am, I had to figure out the probability of that happening b/c it seemed like it would be low to me. Math people check me if I’m wrong but it would be (362/365)^453 where 453 is the number of friends I have. It’s only 2.379%. Not as low as I thought. Then I thought, what’s the probability that one of my friends has a birthday on a leap day (who Carey, actually does). 1/(365+365+365+366) * 453 = 31%. Actually pretty high. Much higher than none of my friends having a birthday 3 days in a row.
Yes, this is what I think about on a Monday morning.