1. The problem statement, all variables and given/known data Let X be the number of different birthdays among four persons selected randomly. Find E(X). 2. Relevant equations 3. The attempt at a solution I am not completely sure how to start this problem. I was thinking of trying to figure out the total number of combinations of four birthdays over 365 days broken into totals showing number of combinations with 1, 2, 3 and 4 unique birthdays. Then divide those totals by the grand total and multiply each by 1, 2, 3 and 4 respectively. But this seemed to blow up. Am I approaching this with the right method or is there a better way?