4-2. For a discrete random variableX, determine the constant k such that f (X) =

k/X, X = 1, 2, 3, 4, 5, is a probability mass function. Then determine:

(a) The cumulative distribution function

(b) P(X ≤ 3)

(c) P(X < 3)

(d) P(1 ≤ X ≤ 4)