Chapter 8.5, Problem 1AC

Testing Gas Mileage Claims

Assume that you are working for the Consumer Protection Agency and have recently been getting complaints about the highway gas mileage of the new Dodge Caravans. Chrysler Corporation agrees to allow you to randomly select 40 of its new Dodge Caravans to test the highway mileage.

Chrysler claims that the Caravans get 28 mpg on the highway. Your results show a mean of 26.7 and a standard deviation of 4.2. You support Chrysler’s claim.

1. Show whether or not you support Chrysler’s claim by listing the P-value from your output. After more complaints, you decide to test the variability of the miles per gallon on the highway. From further questioning of Chrysler’s quality control engineers, you find they are claiming a standard deviation of no more than 2.1. Use a one-tailed test.

2. Test the claim about the standard deviation.

3. Write a short summary of your results and any necessary action that Chrysler must take to remedy customer complaints.

4. State your position about the necessity to perform tests of variability along with tests of the means.