The number of miles of useful tread wear (in 1000s) was determined for tires of each of five different makes of subcompact car (factor A, with ) in combination with each of four different brands of radial tires (factor B, with ), resulting in observations. The values

, and were then computed. Assume that an additive model is appropriate.

SSB 5 44.1 SSE 5 59.2 IJ 5 20 SSA 5 30.6, J 5 4 I 5 5

a. Test (no differences in true average tire lifetime due to makes of cars) versus Ha: at least one using a level .05 test.

b. (no differences in true average tire lifetime due to brands of tires) versus Ha: at least one using a level .05 test.