A random sample of medical files is used to estimate the proportion p of all people who have blood type B.
(a) If you have no preliminary estimate for p, how many medical files should you include in a random sample in order to be 85% sure that the point estimate  will be within a distance of 0.05 from p?
(b) Answer part (a) using a preliminary estimate that about 8 out of 90 people have blood type B.