In a class of 30 students, what is the probability that 2 people have the same birthday?

Answer 1

There is a nice discussion of this and similar problems at

http://mathforum.org/dr.math/faq/faq.birthdayprob.html

as google would have told you.

Answer 2

p=0.1. what is the probability that one person gets it right in a class of 30 students.