Find the probability that among r people, there will be at least one whose birthday is the same as yours ( you may assume no one is born on a leap day, including yourself.

The probability that at least one person has the same birthday as you is equal to one minus the probabilit that no one has the same birthday as you. If r = 1, the probability that he has does not have the same birthday as you is 364/365. If r= 2, then the probability that both people have different birthdays than you is (364/365)^2. Can you take it from here?