1. The problem statement, all variables and given/known data There are 10 sister/brother pairs, (S1,B1) .... , (S10,B10). We then divide the 20 people randomly into 10 (not necessarily female/male) pairs. Let X be the number of female/male pairs. Find E(X) Let Y be the number of pairs consisting of siblings (that is, sister got matched with her brother). Find E(Y) 2. Relevant equations 3. The attempt at a solution I only know how to find out the total number of ways to select 10 pairs, that's (20,2)+(18,2)+(16,2)+.....+(2,2). (x,y) means x choose y Please help. Thanks!!