Medical: Blood Type A random sample of medical fi les 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 fi les should you include in a random sample in order to be 85% sure that the point estimate pˆ will be within a distance of 0.05 from p?

(b) Answer part

(a) if you use the preliminary estimate that about 8 out of 90 people have blood type B (Reference: Manual of Laboratory and Diagnostic Tests by F. Fischbach).