You work in an office of 23 people (includes you)
What is the probability that 2 people in your office have the same birthday?
(Ignore Febuarary 29th)
See here for a detailed explanation :
http://mathforum.org/dr.math/faq/faq.birthdayprob.html
P(2 people out of 23 share the same birthday) =
1 - P (none of the 23 share the same birthday) =
1 - 365! / [ (365 - 23)! * 365^23 ] ≈ .5073 = 50.73%
+2863 
