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 p will be within a distance of 0.07 from p?
______medical files
(b) Answer part (a) if you use the preliminary estimate that about 13 out of 90 people have blood type B.
_______ medical files