38. Tax audits, part 2. While reviewing the sample of audit fees, a senior accountant for the firm notes that the fee charged by the firm’s accountants depends on the complexity of the return. A comparison of actual charges therefore might not provide the information needed to set next year’s fees. To better understand the fee structure, the senior accountant requests a new sample that measures the time the accountants spent on the audit. Last year, the average hours charged per client audit was 3.25 hours. A new sample of 10 audit times shows the following times in hours:

4.2, 3.7, 4.8, 2.9, 3.1, 4.5, 4.2, 4.1, 5.0, 3.4

a) Assume the conditions necessary for inference are met.

Find a 90% confidence interval estimate for the mean audit time.

b) Based on your answer to part

a, comment on the claim that the mean fees have increased.