The percentage of hardwood concentration in raw pulp, the vat pressure, and the cooking time of the pulp are being investigated for their effects on the strength of paper. Three levels of hardwood concentration, three levels of pressure, and two cooking times are selected. A factorial experiment with two replicates is conducted, and the following data are obtained: 

 

(a) Analyze the data and draw conclusions. Use α = 0.05.

(b) Prepare appropriate residual plots and comment on the model's adequacy.

(c) Under what set of conditions would you operate this process? Why?

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Cooking Time 3.0 Hours Cooking Time 4.0 Hours Percentage of Hardwood Pressure Pressure Concentration 400 500 650 400 500 650 196.6 197.7 199.8 198.4 199.6 200.6 196.0 196.0 199.4 198.6 200.4 200.9 4 198.5 196.0 198.4 197.5 198.7 199.6 197.2 196.9 197.6 198.1 198.0 199.0 8 197.5 195.6 197.4 197.6 197.0 198.5 196.6 196.2 198.1 198.4 197.8 199.8