1. The problem statement, all variables and given/known data f(x,y) = x2 + xy3 for 0 < x < 1, 0 < y < 2 and 0 otherwise. Calculate P(X+Y < 1) 2. Relevant equations 3. The attempt at a solution P(X+Y < 1) = P(X < 1-Y) which means y is now bounded by 0:1 instead of 0:2 and x is bounded by 0:y. So we get ∫[0-1]∫[0-y] x2 + xy3 dx dy Integrating twice I get the answer P(X < 1-Y) = 1/8, which is incorrect. What am I doing wrong?