Gas Mileage an Important Factor in the Amount of Gasoline $\quad$

Gas mileage An important factor in the amount of gasoline a car uses is the size of the engine. Called "displacement", engine size measures the volume of the cylinders in cubic inches. The regression analysis is shown.

Dependent variable is: $\quad$ $\quad$ MPG
89 total cases of which 0 are missing
$\mathrm{R}$ squared $=60.9 \% \quad \mathrm{R}$ squared (adjusted) $=60.0 \%$
$s=3.056$ with $89-2=87$ degrees of freedom
$\begin{array}{llrrr}\text { Source } & \text { Sum of Squares } & \text { df } & \text { Mean Square } & \text { F-ratio } \\ \text { Regression } & 696.744 & 1 & 696.744 & 74.6 \\ \text { Residual } & 448.236 & 48 & 9.33826 & \\ & & & & \\ \text { Variable } & \text { Coefficient } & \text { s.e. of Coeff } & \text { t-ratio } & \text { prob } \\ \text { Constant } & 34.9799 & 1.231 & 28.4 & <0.0001 \\ \text { Eng. Displcmt } & -0.066196 & 0.0077 & -8.64 & <0.0001\end{array}$

a. How many cars were included in this analysis?
b. What is the correlation between engine size and fuel economy?
c. A car you are thinking of buying is available with two different size engines, 190 cubic inches or 240 cubic inches. How much difference might this make in your gas mileage? (Show your work.)