In the chapter introduction we presented gas mileage data for 2000 and 2009 model year compact cars. We will use histograms and back-to-back stem-and-leaf plots to compare the mileage between these two groups of cars. The following tables present the mileage in miles per gallon.

Highway Mileage Ratings for 2000 Compact Cars

28           21           30           33           24           29           30           38

27           23           27           34           21           27           38           28

29           21           31           31           32           23           36           28

27           32           31           30           26           23           40           28

27           27           34           28           34           28           38           27

29           27           33           24           31           33           27           28

26           26           31           16           28           30           30           24          

37           35           30           33           31           32

Highway Mileage Ratings for 2009 Compact Cars

30           30           27           15           14           17           28

26           25           34           29           26           25           33

35           35           25           30           25           25           25          

21           17           18           17           21           18           25

34           33           18           18           27           28           30

25           26           31           30           35           29           29

25           29           28           26           28           26           26

25           30           19           22           26           29          

Construct a frequency distribution for the 2000 cars with a class width of 1

Explain why a class width of 1 is too narrow for these data

Construct a relative frequency distribution for the 2000 cars with a class width of 2, where the first class has lower limit of 15

Construct a histogram based on this relative frequency distribution. Is the histogram unimodal or bimodal? Describe the skewness if any in these data.

Construct a frequency distribution for the 2009 cars with an appropriate class width

Using this class width construct a relative frequency distribution for the 2009 cars

Construct a histogram based on this relative frequency distribution. Is the histogram unimodal or bimodal? Describe the skewness if any in these data.

Compare the histogram for the 2000 cars with the histogram for the 2009 cars. Which cars tend to have higher gas milelage?

Construct a back-to-back stem-and-leaf plot for these data using two lines for each stem. Which do you think illustrates the comparison better, the histogram or the back-to-back stem-and-leaf plot? Why?