9.5 Practice

Fuel efficiency: city versus highway Here are the EPA estimates of city gas mileage and highway gas mileage in miles per gallon (mpg) for a sample of 21 model-year 2014 midsize cars.

Model , City , Highway

Acura RLX , 20 , 31

Audi A8 , 18, 28

BMW 550I , 17 , 25

Buick Lacrosse , 18, 28

Cadillac CTS , 18, 27

Chevrolet Malibu, 21, 30

Chrysler 200, 21, 30

Dodge Avenger, 21, 30

Ford Fusion, 22, 31

Hyundai Elantra, 28, 38

Jaguar XF, 19, 30

Kia Optima, 20, 31

Lexus ES 350, 21, 31

Lincoln MKZ, 22, 31

Mazda 6 , 28, 40

Mercedes-Benz E350, 21, 30

Nissan Maxima, 19, 26

Subaru Legacy, 24, 32

Toyota Prius, 51, 48

Volkswagen Passat, 24, 34

Volvo S80, 18, 25

Make a dotplot of the difference (Highway - City) in gas mileage for each car model. What does the graph reveal?

• Only 1 of the difference values is negative, so the highway gas mileage exceeds the city gas mileage for 20 out of the 21 vehicles. The difference values vary from -3 mpg (Toyota Prius) to 12 mpg (Mazda 6)

• Only 1 of the difference values is positve, so the highway gas mileage exceeds the city gas mileage for 20 out of the 21 vehicles. The difference values vary from -3 mpg (Toyota Prius) to 12 mpg (Mazda 6)

• I don't know how to make a dotplot.

• There are no conclusions.

Fuel efficiency: city versus highway Here are the EPA estimates of city gas mileage and highway gas mileage in miles per gallon (mpg) for a sample of 21 model-year 2014 midsize cars.

Model , City , Highway

Acura RLX , 20 , 31

Audi A8 , 18, 28

BMW 550I , 17 , 25

Buick Lacrosse , 18, 28

Cadillac CTS , 18, 27

Chevrolet Malibu, 21, 30

Chrysler 200, 21, 30

Dodge Avenger, 21, 30

Ford Fusion, 22, 31

Hyundai Elantra, 28, 38

Jaguar XF, 19, 30

Kia Optima, 20, 31

Lexus ES 350, 21, 31

Lincoln MKZ, 22, 31

Mazda 6 , 28, 40

Mercedes-Benz E350, 21, 30

Nissan Maxima, 19, 26

Subaru Legacy, 24, 32

Toyota Prius, 51, 48

Volkswagen Passat, 24, 34

Volvo S80, 18, 25

Calculate the mean and interpret the mean difference in context

• x̄_diff = 8.81

  The highway gas mileage for these 21 vehicles is 8.81 mpg higher than the city gas mileage, on average.

• x̄_diff = 2.994

  The highway gas mileage for these 21 vehicles is 2.994 mpg higher than the city gas mileage, on average.

• x̄_diff = 8.81

  The highway gas mileage for these 21 vehicles is 8.81 mpg lower than the city gas mileage, on average.

• x̄_diff = -8.81

  The highway gas mileage for these 21 vehicles is 8.81 mpg lower than the city gas mileage, on average.

Fuel efficiency: city versus highway Here are the EPA estimates of city gas mileage and highway gas mileage in miles per gallon (mpg) for a sample of 21 model-year 2014 midsize cars.

Model , City , Highway

Acura RLX , 20 , 31

Audi A8 , 18, 28

BMW 550I , 17 , 25

Buick Lacrosse , 18, 28

Cadillac CTS , 18, 27

Chevrolet Malibu, 21, 30

Chrysler 200, 21, 30

Dodge Avenger, 21, 30

Ford Fusion, 22, 31

Hyundai Elantra, 28, 38

Jaguar XF, 19, 30

Kia Optima, 20, 31

Lexus ES 350, 21, 31

Lincoln MKZ, 22, 31

Mazda 6 , 28, 40

Mercedes-Benz E350, 21, 30

Nissan Maxima, 19, 26

Subaru Legacy, 24, 32

Toyota Prius, 51, 48

Volkswagen Passat, 24, 34

Volvo S80, 18, 25

Calculate the standard deviation.

• σ_diff = 2.994

• σ_diff = 8.81

• σ_diff = -2.994

• There is no standard deviation.

Fuel efficiency: city versus highway Here are the EPA estimates of city gas mileage and highway gas mileage in miles per gallon (mpg) for a sample of 21 model-year 2014 midsize cars.

Model , City , Highway

Acura RLX , 20 , 31

Audi A8 , 18, 28

BMW 550I , 17 , 25

Buick Lacrosse , 18, 28

Cadillac CTS , 18, 27

Chevrolet Malibu, 21, 30

Chrysler 200, 21, 30

Dodge Avenger, 21, 30

Ford Fusion, 22, 31

Hyundai Elantra, 28, 38

Jaguar XF, 19, 30

Kia Optima, 20, 31

Lexus ES 350, 21, 31

Lincoln MKZ, 22, 31

Mazda 6 , 28, 40

Mercedes-Benz E350, 21, 30

Nissan Maxima, 19, 26

Subaru Legacy, 24, 32

Toyota Prius, 51, 48

Volkswagen Passat, 24, 34

Volvo S80, 18, 25

Calculate and Interpret a 90% confidence interval of the mean difference (Highway - City)

• (7.683, 9.937)

  We are 90% confident that the interval from 7.683 to 9.937 captures the true mean difference (Highway - City) in gas mileage. The interval suggests that Highway mpg is 7.683 to 9.937 higher than City mpg.

• (7, 9)

  We are 90% confident that the interval from 7 to 9 captures the true mean difference (Highway - City) in gas mileage. The interval suggests that Highway mpg is 7 to 9 higher than City mpg.

• (7.683, 9.937)

  We are 90% confident that the interval from 7.683 to 9.937 captures the true mean difference (Highway - City) in gas mileage. The interval suggests that Highway mpg is 7.683 to 9.937 lower than City mpg.

• (7, 9)

  We are 90% confident that the interval from 7 to 9 captures the true mean difference (Highway - City) in gas mileage. The interval suggests that Highway mpg is 7 to 9 lower than City mpg.