Question

National Fuelsaver Corporation manufactures the Platinum Gasaver, a device they claim "may increase gas mileage by 22%." Here are the percent changes in gas mileage for 15 identical vehicles, as presented in one of the company's advertisements:
48.3 46.9 46.8 44.6 40.2 38.5 34.6 33.7
28.7 28.7 24.8 10.8 10.4 6.9 -12.4

Would you recommend use of a t confidence interval to estimate the mean fuel savings in the population of all such vehicles? Explain your answer.

Answer 1

I would use a confidence interval to estimate the mean fuel savings because of the range of the data. If the data were close together, a simple mean would be enough. Here there is a wide spread of values between 48.3 and 6.9. A confidence interval would be a good representation of the values.