2011-06-10, 03:22 PM
1-P(everyone has a different birthday)
Consider person one... he can have any birthday without matching someone
1-365/365 aka 0% 1 person shares a birthday with someone else (makes sense.... there's no one else)
2nd person... any birthday cept the one from the previous person so he has 364/365 options
1- (365*364)/(365*365)
go to 20 people
1- (365*...*346)/(365^20) ~41%
Consider person one... he can have any birthday without matching someone
1-365/365 aka 0% 1 person shares a birthday with someone else (makes sense.... there's no one else)
2nd person... any birthday cept the one from the previous person so he has 364/365 options
1- (365*364)/(365*365)
go to 20 people
1- (365*...*346)/(365^20) ~41%