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?