1. The problem statement, all variables and given/known data Let X be the number of 1's and Y be the number of 2's that occur in n rolls of a fair die. Find Cov(X, Y) 2. Relevant equations Cov(X,Y) = E(XY) - E(X)E(Y) 3. The attempt at a solution Both X and Y are binomial with parameters n and 1/6. Thus it is easy to find E(X) and E(Y), but for some reason finding E(XY) is really tripping me up. How does one go about finding expected values of products of binomial variables?