Robert Altoff is vice president of engineering for a manufacturer of household washing machines. As part of a new product development project, he wishes to determine the optimal length of time for the washing cycle. Included in the project is a study of 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 amounts 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 here:

Detergent BrandCycle Time (min)18202224A0.130.140.140.130.150.150.140.13B0.160.150.150.160.140.150.150.15C0.170.180.160.170.170.160.170.18D0.120.130.130.130.140.130.130.13