Fuel Consumption Most cars are fuel efficient when running at a steady speed of around 40 to 50 mph. A scatterplot relating fuel consumption (measured in mpg) and steady driving speed (measured in mph) for a mid-sized car is shown below. The data are available in the Fuel file on the book’s Web site. (Source: Berry, I. M. (2010). The Effects of Driving Style and Vehicle Performance on the Real-World Fuel Consumption of U.S. Light-Duty Vehicles.

Masters thesis, Massachusetts Institute of Technology, Cambridge, MA.)

a. The correlation equals 0.106. Comment on the use of the correlation coefficient as a measure for the association between fuel consumption and steady driving speed.

b. Comment on the use of the regression equation as a tool for predicting fuel consumption from the velocity of the car.

c. Over what subrange of steady driving speed might fitting a regression equation be appropriate? Why?

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Fuel Consumpt. (mpg) 50 Fuel Consumption vs. Speed 40 30 20 10 0 5 15 25 35 45 55 65 75 85 Steady Driving Speed (mph)