Following 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.)

(a) Fit the model Y01x2x2using least squares.

(b) Test for significance of regression using 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 a t-test. If 0.05, what conclusion can you draw?

(d) Plot the residuals from the model in part

(a) versus . Does the plot reveal any inadequacies?

(e) Construct a normal probability plot of the residuals.
Comment on the normality assumption.

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