Help

#1
I have absolutly no idea where to start with this question. what is the probability that 2 people out of 40 have the same birthday? HELP
 
#2
Think about this, then. What is the probability that NOBODY out of 40 have the same birthday?

Does the problem ask for the probability that at least 2 have the same birthday, or exactly 2? Anyway, think about the problem above and that might help.