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*n*people. Assuming that days of the year are equally likely to be birthdays for each person, calculate the probability that at least two of the people have a common birthday.

well I have the answer but I'm just curious as to the thought processes you go through to answer it.

what ive done (incorrectly) is:

if n = 2, P = 1/365^2

if n = 3, P = 1/365^2 (person 1, 2) + 1/365^2 (person 1, 3) + 1/365^2 (person 2, 3)

and generalized it to:

( 3 + (n sum i=3) (i)! / (i-1)! ) / 365^2

there's no question that it's wrong but thats the process I take