A researcher conducts a mileage economy test involving 80 cars. The frequency distribution describing average miles per gallon (mpg) appears in the following table.
Average mpg ..... Frequency
15 up to 20 ...... 15
20 up to 25 ...... 30
25 up to 30 ...... 15
30 up to 35 ...... 10
35 up to 40...... 7
40 up to 45 ...... 3

a. Construct the corresponding relative frequency, cumulative frequency, and cumulative relative frequency distributions.
b. How many of the cars got less than 30 mpg? What percentage of the cars got at least 20 but less than 25 mpg? What percentage of the cars got less than 35 mpg? What percent got 35 mpg or more?
c. Construct a histogram. Comment on the shape of the distribution.