Below are data on y = green liquor (g/l) and x = paper machine speed

(ft/min) from a kraft paper machine. (The data were read from a graph in an article in the Tappi Journal , March 1986.)

y 16.0 15.8 15.6 15.5 14.8 x 1700 1720 1730 1740 1750 y 14.0 13.5 13.0 12.0 11.0 x 1760 1770 1780 1790 1795

a. Fit the model y = β0 + β1x + β2x2 + ε to the data.

b. Test for signifi cance of regression using α = 0.05. What are your conclusions?

c. Test the contribution of the quadratic term to the model, the contribution of the linear term, using an F statistic. If α = 0.05, what conclusion can you draw?

d. Plot the residuals from the model. Does the model fi t seem satisfactory?