An article in Tappi (1960, Vol. 43, pp. 3844) describes an experiment that investigated

Chapter 14, Problem 14-57

(choose chapter or problem)

An article in Tappi (1960, Vol. 43, pp. 3844) 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 . x1 1T 7752 115 , x2 1t 32 1.5 y2 23 3x1 4x2 y1 10 5x1 2x2 y 50 1.5x1 0.8x2 x1 x2 y x1 x2 y 1 1 211 0 1.5 168 1 1 92 0 1.5 179 1 1 216 0 0 122 1 1 99 0 0 175 1.5 0 222 0 0 157 1.5 0 48 0 0 146 (a) What type of design has been used in this study? Is the design rotatable? (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? 14-58. In the