The mean costs (in current dollars) of tuition, fees, room, and board at four-year public colleges are shown in Table 4 for various years.
Table 4
Mean Costs (in Current Dollars) of Tuition, Fees, Room, and Board
Year Mean Cost (dollars)
1975 ………………………… 1646
1980 ………………………… 2328
1985 ………………………… 3682
1990 ………………………… 4715
1995 ………………………… 6620
2000 ………………………… 8080
2005 …………………………11,376
2010 …………………………15,235
2015 …………………………18,943
Let y be the mean cost (in current dollars) of tuition, fees, room, and board at four-year public colleges at x years since 1970.
a. Construct a scatterplot.
b. Is there a linear association, a nonlinear association, or no association?
c. Use technology to graph the equation  = 1338(1.063)x on the scatterplot. Does the model come close to the data points?
d. Use the model to estimate the cost in 2015. Compute the residual for your estimate.
e. Some public four-year colleges in Indiana, Iowa, Minnesota, and Missouri froze their tuitions in 2015. Why is it not surprising that the residual you found in part (d) is negative?