An article in Rubber Age (Vol. 89, 1961, pp. 453–458) describes an experiment on the manufacture of a product in which two factors were varied: reaction time (hr) and temperature (°C). These factors are coded as x1 = (time 12)8 and x2 = (temperature 250)30. The following data were observed where y is the yield (in percent).
(a) Plot the points at which the experimental runs were made.
(b) Fit a second-order model to the data. Is the second-order model adequate?
(c) Plot the yield response surface. What recommendations would you make about the operating conditions for this process?