The manager of an auto repair wants to advertise one price for an engine tune-up, with parts included. Before he decides the price to advertise, he needs a good estimate of the average cost of tune-up parts. A sample of 20 customer invoices for tune-ups has been selected and the costs of parts, rounded to the nearest dollar, are listed below. Answer the three questions below. 23 24 25 26 80 150 104 78 74 93 62 57 68 75 97 52 73 99 77 105 80 62 109 27 65 28 29

Required:
a. What is the point estimate for the average cost of all tune-up parts?
b. 99% confidence interval is: