A 24 factorial design has been run in a pilot plant to investigate the effect of four factors on the molecular weight of a polymer. The data from this experiment are as follows (values are coded by dividing by 10).

a. Construct a normal probability plot of the effects. Which effects are active?
b. Construct an appropriate model. Fit this model and test for significant effects.
c. Analyze the residuals from this model by constructing a normal probability plot of the residuals and plotting the residuals versus the predicted values of y.

(1) 88 d 86 a 80 ad 81 b 89 bd 85 ab 87 abd 86 86 cd 85 ac 81 acd 79 bc 82 cd 84 abc 80 abcd 81