When buying or leasing a new car, one of the factors that customers consider is the type of fuel it uses. Some people prefer vehicles that use diesel fuel, while others favor vehicles that use regular unleaded gasoline. Which of these two types of fuel costs more at the pump, on average? Does the answer to this question depend on the state where you live?

Researchers collected data on the price per gallon (in dollars) of diesel fuel and regular unleaded gasoline from a random sample of gas stations in 6 states: Colorado, Illinois, Indiana, Kansas, Missouri, and Ohio. The file gas prices ch 10 project.xls, which can be accessed from the book’s website at highschool.bfwpub.com/tps6e, contains data from a total of 82 gas stations. Download the file to a computer for further analysis using the application specified by your teacher. Use the file provided to answer the following questions.

1. Start by calculating the difference (Diesel – Unleaded) in gas prices for all 82 stations, and store these values in a new column titled Difference.

2. Make a graph to display the distribution of difference in gas prices. Describe the shape, center, and variability of the distribution. Are there any outliers?

3. Construct and interpret a 95% confidence interval for the true mean difference. Does the interval provide convincing evidence of a difference in the mean price per gallon of diesel fuel and regular unleaded gasoline?

4. Make a graph that compares the difference (Diesel − Unleaded) in gas prices for the 6 states from which the data were collected. Write a few sentences comparing the distributions.

5. We might expect the mean difference (Diesel − Unleaded) in gas prices to be the same for adjacent states. Choose 2 adjacent states from the data set. Then carry out an appropriate test to see if the data provide convincing evidence to contradict this expectation.