Following are data on y = green liquor (g/l) and x = paper machine speed (feet per minute) from a Kraft paper machine. (The data were read from a graph in an article in the Tappi Journal, March 1986)

a) Fit the model Y = BO + B1x + B2x2 + E using least squares.
(b) Test for significance of regression using a = 0.05. What are your conclusions?
(c) Test the contribution of the quadratic term to the model, over the contribution of the linear term, using an F-statistic. If a = 0.05, what conclusion can you draw?
(d) Plot the residuals from the model in part (a) versus y. Does the plot reveal any inadequacies?
(e) Construct a normal probability plot of the residuals. Comment on the normality assumption.

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