8.68 Twenty-five blood samples were selected by taking every seventh blood sample from racks holding 187 blood samples from the morning draw at a medical center. The white blood count (WBC) was measured using a Coulter Counter Model S. The mean WBC was 8.636 with a standard deviation of 3.9265.
(a) Construct a 90 percent confidence interval for the true mean using the FPCF.
(b) What sample size would be needed for an error of ±1.5 with 90 percent confidence? (Data are from a project by MBA student Wendy Blomquist.)