Gas Mileage Again in the Data Desk Lab Last Week $= 60.9 \% \quad$

question 762

Essay

Gas mileage again In the Data Desk lab last week you analyzed the association between a
car's fuel economy and its weight. Another 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:
MPG
89 total cases of which 0 are missing
R squared $= 60.9 \% \quad$ R squared (adjusted) $= 60.0 \%$
$s = 3.056$ with $89 - 2 = 87$ degrees of freedom


$\begin{array}{llrrr}\text { Source } & \text { Sum of Squares } & \text { df } & \text { Mean Square } & \text { F-ratio } \\\text { Regression } & 696.744 & 1 & 696.744 & 74.6 \\\text { Residual } & 448.236 & 48 & 9.33826 &\end{array}$

$\begin{array}{lllll}\text { Variable } & \text { Coefficient } & \text { s.e. of Coeff } & \text { t-ratio } & \text { prob } \\\text { Constant } & 34.9799 & 1.231 & 28.4 & \text { Ş } 0.0001 \\\text { Eng. Displemt } & -0.066196 & 0.0077 & -8.64 & \text { S } 0.0001\end{array}$



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 work)

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