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 80% sure that the point estimate phatitalic will be within a distance of 0.052 from p?
(b) Answer part (a) if you use the preliminary estimate that about 9 out of 90 people have blood type B.