The Manager of Hudson Auto Repair Wants to Advertise One

Short Answer

The manager of Hudson 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 taken and the costs of parts, rounded to the nearest dollar, are listed below.
Provide a 90% confidence interval estimate of the mean cost of parts per tune-up for all of the tune-ups performed at Hudson Auto Repair.