Question

We expect a car's highway gas mileage to be related to its city gas mileage (in miles per gallon, mpg). Data for all 1137 vehicles in the government's 2013 Fuel Economy Guide give the regression line

highway mpg = 6.785 + (1.033 × city mpg)

for predicting highway mileage from city mileage.

(a) What is the slope of this line? (Enter your answer to three decimal places.)
____mpg

Say in words what the numerical value of the slope tells us.

-On the average, highway mileage decreases by 1.033 mpg for each additional mpg in city mileage.

-Highway gas mileage increases with city gas mileage by 6.785 mpg for each additional mpg in city mileage.     

-On the average, highway mileage increases by 6.785 mpg for each additional mpg in city mileage

-For every 6.785 mpg in city gas mileage, highway gas mileage increases about 1.033 mpg.

-On the average, highway mileage increases by 1.033 mpg for each additional mpg in city mileage.

(b) What is the intercept? (Enter your answer to three decimal places.)
mpg

Explain why the value of the intercept is not statistically meaningful.

-Because this is an average value, calculated from a sample.

-Because this is the highway mileage for zero city mpg.    

- Because this is the highway mileage for slope 0.

(c) Find the predicted highway mileage for a car that gets 18 miles per gallon in the city. (Round your answer to two decimal places.)
______ mpg

Find the predicted highway mileage for a car that gets 25 miles per gallon in the city. (Round your answer to two decimal places.)
______ mpg

(d) Draw a graph of the regression line for city mileages between 10 and 50 mpg. (Be sure to show the scales for the x and y axes.)

Answer 1

a) slope of this line=1.033

-On the average, highway mileage increases by 1.033 mpg for each additional mpg in city mileage

b)intercept=6.785

Because this is the highway mileage for zero city mpg.    

c)

predicted highway mileage for a car that gets 18 miles per gallon in the city=6.785+1.033*18=25.38

predicted highway mileage for a car that gets 25 miles per gallon in the city=6.785+1.033*25=32.61

d)