The graph on page 162 shows the relationship between three variables: number of licensed drivers, number of registered vehicles, and the size of the resident population in the United States from 1960 to 2007. Study the graph and answer the questions.
a. Does it seem reasonable for the population line and the drivers line to basically parallel each other, with the population line above the drivers line? Explain what it means for them to be parallel.What would it mean if they were not parallel?
b. What does it mean that the drivers and motor vehicles lines cross? When and what does the point of intersection represent?
c. Explain the relationship between motor vehicles and drivers before 1973.
d. Explain the relationship between motor vehicles and drivers after 1973.
e. Do you predict drivers ever surpassing motor vehicles after 2007? Why or why not?
f. Using the years 1990 and 2002, estimate the slopes of the motor vehicles line and the drivers line. Compare and contrast the slopes found.

Licensed Drivers, Vehicle Registrations, and Resident Population 310 260 210 2 160 110 Popula hion Motor Vehicles Drivers 601 1960 1966 1972 1978 1984 1990 1996 2002 2008 Year