4.6 Fuel efficiency of Prius. Fueleconomy.gov, the official US government source for fuel econ-

omy information, allows users to share gas mileage information on their vehicles. The histogram

below shows the distribution of gas mileage in miles per gallon (MPG) from 14 users who drive a

2012 Toyota Prius. The sample mean is 53.3 MPG and the standard deviation is 5.2 MPG. Note

that these data are user estimates and since the source data cannot be verified, the accuracy of

these estimates are not guaranteed.

(a) We would like to use these data to evaluate the average gas mileage of all 2012 Prius drivers.

Do you think this is reasonable? Why or why not?

(b) The EPA claims that a 2012 Prius gets 50 MPG (city and highway mileage combined). Do

these data provide strong evidence against this estimate for drivers who participate on fuele-

conomy.gov? Note any assumptions you must make as you proceed with the test.

(c) Calculate a 95% confidence interval for the average gas mileage of a 2012 Prius by drivers who

participate on fueleconomy.gov.