How many friends must you have to guarantee that at least five of them will have birthdays in the same month?

Answer 1

p(at least 5 have the same month)
p(someone shows w/ at least someone else)

P(s)+ P(d) = 100 %
100%- P(d)
(12 *11*10*9*8)/12^5
P(d) =95040/248832 = .3819
100% -0.3819 = 0.6181

61.81%

Answer 2

16