Three percent of the letters placed in a certain postal drop box have incorrect postage. Suppose 200 letters are mailed.
(a) For this binomial, what is the expected number with incorrect postage?
(b) For this binomial, what is the standard deviation?
(c) What is the approximate probability that at least 10 letters will have incorrect postage?
(d) Fewer than five?
(e) Is the Poisson approximation justified?