The primary property of the alloys used for teeth filling is the percent of shrinkage on drying. For a certain alloy 45 test specimens showed an average shrinkage percentage of 18.4 and a variance of 1.44.
a. Estimate the true average percentage of shrinkage for specimens of this type in a 98% confidence interval.
b. How large a sample size is necessary if the length of 98% interval is to be 0.4?