Problems 11-12. Repair Costs: Computers. In a random sample ot 20 computers, the mean repair cost was S142_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 tor the population mean 12. What is the margin of error, E? Problems 13-15. Sa/aryes The monthly incomes for 14 randomly selected people, each witn a bachelors degree were gathered. Assume that the population ot the monthly incomes is normally distributed. use the data in Table 1 to answer the questions. Table 1. The monthly incomes of 14 randomly selected people with a bachelor's degree Salaries Dollars 6399.84 6107.86 13. What is the sample mean, i? 14. What is the sample standard deviation, s? 15. Construct a 90% confidence interval tor the population mean g. Section 6.3 7072.61 7521.89 5847.37 6540.86 6746.40 7063.97 7344.15 7045.74 7091.05 7637.07 631274 8049.48 Problems 16-17. Let p be the population propoion. In a survey ot 5218 LI.S. adults, 3642 say they nave contributed to a charity in the past 12 months. Round results to 3 decimal places. 16. What is the point estimate, D, tor p? 17. What is the point estimate, Q, tor q? Problems 18-19. Let p be the population propoion. In a survey ot 2248 LI.S. adults, 679 say they would go on vacation to Europe it cost did not matter. Round results to 3 decimal places. 1 & What is the point estimate, p, tor p? 19. What is the point estimate, 4 , tor q? problems 20-22. In a survey ot 5350 LIS. adults, 427 say they have traveled out ot country in the past 12 months. Round your results to 3 decimal places. 20. Construct the 95% confidence interval tor the population proportion p. 21. Construct the 99% confidence interval tor the population proportion p. 22. Which of the two intervals you found is narrowen (Suggestion: plot the interval boundaries on a number line.) Problems 23-25. Online Service Usage. You are a travel agent and Wisn to estimate, witn 92% confidence, the proportion of vacationers who use an online service or the internet to make travel reservations. Your estimate must be accurate to within 5% ot the population proportiom (Note: Do not use the c value tor 90% or 95% to approximate the solution. use the characteristics ot c to find the best value tor a 92% level ot confidence. See FAQ 4.11 23. Assume that no preliminary estimate is available. Find the minimum sample size needed. 24. Find the minimum sample size needed, using a prior study that found that 40% of the respondents said they used an online service or the internet to make travel reservations. 25. What do you conclude about the effects ot having a preliminary estimate based on your results tound in questions 23 and 24?