12.14 Transportation Research, Inc., has asked you to prepare some multiple regression equations to estimate the effect of variables on vehicle horsepower.

The data for this study are contained in the data file Motors, and the dependent variable is vehicle horsepower—

horsepower—as established by the Department of Transportation certification.

a. Prepare a regression equation that uses vehicle weight—weight—and cubic inches of cylinder displacement—

displacement—as predictor variables.

Interpret the coefficients.

b. Prepare a regression equation that uses vehicle weight, cylinder displacement, and number of cylinders—

cylinder—as predictor variables. Interpret the coefficients and compare the results with those in part a.

c. Prepare a regression equation that uses vehicle weight, cylinder displacement, and miles per gallon—milpgal—

as predictor variables. Interpret the coefficients and compare the results with those in part a.

d. Prepare a regression equation that uses vehicle weight, cylinder displacement, miles per gallon, and price as predictor variables. Interpret the coefficients and compare the results with those in part c.

e. Write a short report that presents the results of your analysis of this problem.