39. The amount of beryllium in a substance is often determined by the use of a photometric filtration method. If the weight of the beryllium is μ, then the value given by the photometric filtration method is normally distributed with mean μ and standard deviation σ. A total of eight independent measurements of 3.180 mg of beryllium gave the following results.

3.166, 3.192, 3.175, 3.180, 3.182, 3.171, 3.184, 3.177 Use the preceding data to

(a) estimate σ;

(b) find a 90 percent confidence interval estimate of σ.