A group of Science Summer Camp students are studying length of minnows in Grand Lake. They take a random sample of 22 minnows and find they have a mean of 7.0 cm and a standard deviation of 2.0 cm. Can you help them out by finding a 99% confidence interval estimate for the population standard deviation of the lengths? (Assume that the lengths of minnows in Grand Lake are normally distributed.) Solution Given a=0.01, chisquare with 0.005,df=n-1=21 is 8.03 (check chisquare table) chisquare 0.995, df=21 is 41.4(check chisquare table) So 99% CI is ((n-1)*s/41.4, (n-1)*s/8.03) --> (sqrt(21)*2/41.4, sqrt(21)*2/8.03) --> (0.2213805, 1.141364).