Problems 11-12. Repair Costs: Computers. In a random sample of 20 computers, the mean repair cost was $142.40 and the standard deviation was $33.65. Assume the repair cost is normally distributed.

11. Use a t-distribution to construct a 99% confidence interval for the population mean .

12. What is the margin of error, EE?

Problems 13-15. Salaries. The monthly incomes for 14 randomly selected people, each with a bachelor's degree were gathered. Assume that the population of the monthly incomes is normally distributed. Use the data in Table 1 to answer the questions.

Salaries (Dollars)
6399.84	7072.61	5847.37	6746.40	7344.15	7091.05	6312.74
6107.86	7521.89	6540.86	7063.97	7045.74	7637.07	8049.48

13. What is the sample mean, xx?

14. What is the sample standard deviation, ss?

15. Construct a 90% confidence interval for the population mean .

Section 6.3

Problems 16-17. Let pp be the population proportion. In a survey of 5218 U.S. adults, 3642 say they have contributed to a charity in the past 12 months. Round results to 3 decimal places.

16. What is the point estimate, ^pp^, for pp?

17. What is the point estimate, ^qq^, for qq?