7. For the joint density fx, Y(i, j) = 80 20 with marginal densities fx (i) = fr() = () (202 ,) 80 20 we derived the conditional expectation B(YIX)(i) = 8 (20 - i) 72 Direct computation gives 8 BY = Eif () = 2. j-0 Theorem 2.5 states that 8 BY = [8(Y X)] = >