Automobile insurance companies use statistics to determine their premiums. The premiums are proportional to the risks and costs of accidents. Suppose that an economist conducted a study that looked at miles driven in the previous year, ages of the drivers, and their gender. The age categories are 16–19, 20–34, 35–54, 55–64, and 65+. Because of the design of the experiment there were 20 observations for each age category–gender combination.

a. Is there enough evidence to conclude that male and female drivers differ in the number of miles they drive?

b. Can we infer that there are differences between the age categories in the number of miles they drive?