1. The problem statement, all variables and given/known data if x1 and x2 are dependent, and y1 and y2 are dependent, but all the x are independent of all the y. Then how can one simplify E(x1y1x2y2)? the textbook says E(x1x2)E(y1y2) So is the rule that you can not just seperate two independent variables which they are multiplied with a third variable which are dependent on the first variable? But you can seperate a group of variables which all the elements in the first group is independent of all the elements in the other group?