1. A telephone company wants to estimate the average length of long-distance calls during weekends. A random sample of 50 calls gives a mean x = 14.5 minutes and standard deviation s = 5.6 minutes. Give a 95% con?dence interval and a 90% con?- dence interval for the average length of a long-distance phone call during weekends.
2. An insurance company handling malpractice cases is interested in estimating the average amount of claims against physicians of a certain specialty. The company obtains a random sample of 165 claims and ?nds x = $16,530 and s = $5,542. Give a 95% con?dence interval and a 99% con?dence interval for the average amount of a claim.