Two- Way ANOVA

Product development engineers and marketers at a household washing machine manufacturing firm want to determine the optimal length of time for a washing cycle.Part of the study includes understanding the relationship between the detergent used (four brands) and the length of the washing cycle (18, 20, 22, or 24 minutes).In order to run the experiment, 32 standard household laundry loads (having equal amount of dirt and the same total weights) are randomly assigned to the 16 detergent-washing cycle combinations.The results (in pounds of dirt removed) are shown below.(Note: The higher the number, the more dirt removed).

a)Draw an interaction plot of the detergent means by cycle time.

b)Compute the ANOVA using Excel and, using the 0.05 significance level, test the interaction effect of brand and cycle time on "dirt removed."

c)Based on your results in part (b), conduct the appropriate tests of hypotheses for differences in factor means.