Let (X,Y)(X, Y)(X,Y) have joint PDF f(x,y)=2f(x,y) = 2f(x,y)=2 for 0≤x≤y≤10 \le x \le y \le 10≤x≤y≤1. What is E[X]E[X]E[X]?
1/4
1/3
1/2
2/3