An insurance company offers its policyholders a number of different premium payment options. For a randomly selected policyholder, let X = the number of months between successive payments. The cdf of X is as follows:
F(x) =
0, x < 1
0.38, 1 <= x < 3
0.49, 3 <= x < 4
0.53, 4 <= x < 6
0.87, 6 <= x < 12
1, 12 <= x
(a) What is the pmf of X?
(b) Using just the cdf, compute P(3 <= X <= 6) and P(4 <= X).