Including February 29th how many different birthdays can there be? Start with any 3 people A, B and C. What is the probability that B has a different birthday from A? What is the probability that A and B have different birthdays and C has a different birthday from A and from B?
For a group of 3 people what is the probability that two will have the same birthday?
What about a group of 4 people? Or a bigger group?
Can you do the calculations to work out the probabilities?