The article "Factorial Design for Column Flotation of Phosphate Wastes" (N. Abdel-Khalek, Particulate Science and Technology, 2000:57-70) describes a 23 factorial design to investigate the effect of superficial air velocity (A), frothier concentration (B), and superficial wash water velocity (C) on the percent recovery of P2O5. There were two replicates. The data are presented in the following table.

a. Compute estimates of the main effects and interactions, along with their sums of squares and P-values. b. Which factors seem to be most important? Do the important factors interact? Explain.

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Percent Recovery -1 56.30 54.85 70.10 72.70 65.60 63.60 80.20 78.80 50.30 48.95 65.30 66.00 60.53 59.50 70.63 69.86 -1 1 -1 1 -1 -1 1 -1 -1