1. The problem statement, all variables and given/known data Suppose that ∫X,Y(x,y) = λ2e-λ(x+y), 0 ≤ x, 0 ≤ y Find E(X + Y) 2. Relevant equations E(X + Y) = E(X) + E(Y) 3. The attempt at a solution Since the expected vale of a sum is the sum of the expected values, I attempted to find the marginal pdfs of the joint pdf. But when calculating the integral for the marginal probability of X, pX(x) = ∫λ2e-λ(x+y) dy from 0 to ∞, the result is an undefined statement, division by zero.