An agricultural experiment designed to assess differences in yields of com for four differ- ent varieties, using three different fertilizers, produced the results (in bushels per acre) shown in the table. FERTILIZER VARIETY A B C D 123 *S* 86 88 92 91 75 80 323 77 81 83 #3% 84 93 79

(a) Set out the two-way analysis of variance table.

(b) Test the null hypothesis that the population mean yields are identical for all four vari- eties of corn.

(c) Test the null hypothesis that population mean yields are the same for all three brands of fertilizer.