Question

“Flora Lube” is a regional chain that provides a standard service for performing oil changes and basic checkups on automobiles. The chain has a standard that says the average time per car for this service should be 12.5 minutes. There is considerable variability in times due to differences in layout of engines, degree of time pressure from other jobs, and many other sources. As a result, the management of the chain decided to study if the standard is being met and randomly selected 30 oil change and basic checkup services within a month and carefully recorded the time they took in minutes. The resulting data are reported in the following table.

11.2	8.1	16.5	18	10.4	12.1	13.2	8.2	13.3	35.1	24.1	12.1	7.5	12.3	15.2
8.8	15.0	9.3	9.0	10.1	14.1	17.3	13.7	12.8	12.8	19.8	22.2	8.3	28.3	11.7

Using the given data and at 3% level of significance, please test whether the chain is achieving its stated standard for the average time for oil change and basic checkup services. Show the necessary steps and explain your conclusion. Is your test result consistent with the conclusion you arrived at based on the 97% confidence interval you constructed under question (a) above? Please explain.        

Answer 1