Suppose the porosity (in %) of coal samples taken from the (now closed) Prince Mine atPoint Aconi, Nova Scotia was found to be normally distributed with = 0.85 %.

a.) Compute a 90 % confidence interval for the true mean porosity of Prince Mine coalif a sample of 25 specimens had an average porosity of 3.65 %.(Give decimal answer to two places past decimal.)

Lower bound:Upper bound:

b.) How large a sample size is necessary if the width of the 90 % CI is to be 0.35?(Give whole number answer.)

c.) What sample size is necessary to estimate the true mean porosity to within 0.25 (ie with half width 0.25)with 95% confidence?(Give whole number answer.)