22. A local department store wants to determine the average age of the adults in the existing marketing area to help target its advertising. A random sampling of 400 adults is selected. The sample mean age is found to be 35 years with a sample standard deviation of 5 years. Construct a 95% confidence interval estimate of the population average age of the adults in the area.

23. The management of a manufacturing plant is studying the number of times employees in a large population of workers are absent. A random sample of 25 employees is chosen and the average number of annual absences per employee in the sample is found to be 6. The sample standard deviation is 0.6. Assuming the population of absences is normally distributed, construct a 99% confidence interval estimate of the population average number of absences.

24. A quality control inspector is concerned with the average amount of weight that can be held by a type of steel beam. A random sample of 5 beams is tested with the following amounts of weight added before the beams begin to show stress (in thousands of pounds): 9, 11, 10, 10, 8. Assuming that the population of weight is normally distributed, construct a 95% confidence interval estimate of the population average weight that can be held.