Question

The article “Evaluating Tunnel kiln Performance” (Amer. Ceramic Soc. Bull., Aug. 1997: 59–63) gave the following summary information for fracture strengths (Mpa) of n = 169 ceramic bars fired in a particular kiln: ¯ x = 89.10, s = 3.73.

(a) Calculate a (two-sided) confidence interval for the true average fracture strength using a confidence level of 90%.

(b) Suppose the investigators had believed a priori that the population standard deviation was about 4 Mpa. Based on this supposition, how large a sample would have been required to estimate µ to within 0.25 Mpa with 95% confidence?

Answer 1