Suppose that X is a discrete random variable with possible values {1, 2, ...}, and probability mass function. pX(k) = c k(k+1) with some constant c > 0. (a) What is the value of c? Hint: 1 k(k+1) = 1 k − 1 k+1 . (b) Find E(X). Hint: Example D.5 could be helpful.