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

question 159

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) $= 60.0 \%$
$\mathrm { s } = 3.056$ with $89 - 2 = 87$ degrees of freedom

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

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


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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Definitions:

Supply Curve

A graphical representation showing the relationship between the price of a good and the quantity of the good that producers are willing to supply.

Economic Profits

The difference between total revenue and total costs, including both explicit and implicit costs, representing the excess returns over the firm's opportunity costs.

Total Profit

The financial gain obtained when total revenue exceeds total expenses from business operations.

Graph

A diagram representing data visually, using lines, bars, or other symbols.