A production process produces items, of which 6% are defective. A random sample of 160 items is selected every day and the number of defective items, say X, is counted. Using the normal approximation to the binomial, find the following:
(a) P(X <=15).
(b) P(X = 13).
(c) P(10 <= X <=16).
(d) P(X = 12).