1. An executive placement service needs to estimate the average salary of exec- utives placed in a given industry. A random sample of 40 executives gives x = $42,539 and s = $11,690. Give a 90% con?dence interval for the average salary of an executive placed in this industry.

2. The following is a random sample of the wealth, in billions of U.S. dollars, of individuals listed on the Forbes "Billionaires" list for 2007.8

2.1, 5.8, 7.3, 33.0, 2.0, 8.4, 11.0, 18.4, 4.3, 4.5, 6.0, 13.3, 12.8, 3.6, 2.4, 1.0

Construct a 90% con?dence interval for the average wealth in $ billions for the people on the Forbes list.

3. For advertising purposes, the Beef Industry Council needs to estimate the average caloric content of 3-ounce top loin steak cuts. A random sample of 400 pieces gives a sample mean of 212 calories and a sample standard deviation of 38 calories. Give a 95% con?dence interval for the average caloric content of a 3-ounce cut of top loin steak. Also give a 98% con?dence interval for the average caloric content of a cut.