3. At a local car rental company, a sample of 200 calls from a customer service line was taken and found that callers were kept waiting on average 12 minutes . The historic population standard deviation is 4 minutes . Do not use Minitab and show all of your calculations a. Calculate a 90 % confidence interval for the true population mean wait time for callers b. Interpret for management the 90 % confidence interval c. How can a manager at this company use this information ? Be specific 4. The data set Advertising $ (on Canvas under data files ) contains the annual advertising expenditures (in millions ) for a sample of 25 companies in the automotive sector and 25 companies in the department store sector. Use this data set to answer the following questions (assume the population is normally distributed ): a. Describe the target population (s). b. Briefly describe a possible sampling frame C. What are the sample mean , standard deviation , median , minimum , and maximum for each sector ? Use Minitab and paste only these descriptive statistics d. Find the best point estimate of the population mean advertising spend for each sector . e. Find the best estimate of the population mean advertising spend for each sector . (Be 95% confident of the answer you give ) First compute using the formula and show your work . Then use Minitab and paste your output below. f. Interpret your estimations in part f. g. Does the assumption of normality for the population appear to be justified in this case ? Why or why not? Paste the graph used to answer this question h. For your solution to part (f), do you have to assume that the each population is normally distributed in order to have confidence in the confidence intervals ? Why or why not? i. Briefly discuss the source and magnitude of sampling error for each sector j. Explain why the margins of error are different for the automotive sector compared to department store sector in this data set k. How can the margin of error be reduced