A manufacturer of laundry products is investigating the performance of a newly formulated stain remover. The new formulation is compared to the original formulation with respect to its ability to remove a standard tomato-like stain in a test article of cotton cloth using a factorial experiment. The other factors in the experiment are the number of times the test article iswashed (1 or 2) and whether or not a detergent booster is used. The response variable is the stain shade after washing

(12 is the darkest, 0 is the lightest). The data are shown in the following table.

Number of Washings Number of Washings 1 2 Formulation Booster Booster Yes No Yes No New 6, 5 6, 5 3, 2 4, 1 Original 10, 9 11, 11 10, 9 9, 10

(a) Conduct an analysis of variance. Using ???? = 0.05, what conclusions can you draw?

(b) Investigate model adequacy by plotting the residuals.