An article in Tappi (Vol. 43, 1960, pp. 38–44)

describes an experiment that investigated the ash value of paper pulp (a measure of inorganic impurities). Two variables, temperature T in degrees Celsius and time t in hours, were studied, and some of the results are shown in the following table. The coded predictor variables shown are

and the response y is (dry ash value in %)
103.

(a) What type of design has been used in this study? Can the design be rotated?

(b) Fit a quadratic model to the data. Is this model satisfactory?

(c) If it is important to minimize the ash value, where would you run the process?

Transcribed Image Text:

x1 (T-775) 115 = (t-3) 1.5