The following data show the costs charged by a tax preparation service for a random sample of 15 tax returns. These data can also be found in the Excel file titled tax prep costs.xlsx.

$135 $120 $150 $110 $90

$115 $130 $200 $180 $200

$140 $150 $100 $75 $70

a. Using a 98% confidence interval, estimate the average cost of the service for preparing a tax return for a customer.

b. What is the margin of error for this sample?

c. Verify your result using Excel.

d. What assumptions are necessary for this analysis?

AppendixLO1