An article gave the following summary information for fractu

An article gave the following summary information for fracture strengths (MPa) of n = 144 ceramic bars fired in a particular kiln: x = 68.54, s = 3.81.

(a) Calculate a (two-sided) confidence interval for true average fracture strength using a confidence level of 95%. (Round your answers to two decimal places.)

(b) Suppose the investigators had believed a priori that the population standard deviation was about 6 MPa. Based on this supposition, how large a sample would have been required to estimate to within 0.5 MPa with 95% confidence?

Solution