15.31 In Greece, an agricultural experiment designed to assess differences in yields of olives for four different varieties (Athenolia, Black olives, Green olives, and Koroneiki), using six different fertilizers, produced the results (in kilos per acre) shown in the following table:

Fertilizer Athenolia Black Green Koroneiki 1 23 22 21 22 2 22 22 24 27 3 17 21 20 28 4 23 20 24 28 5 19 22 21 23 6 22 20 22 29

a. Prepare the two-way analysis of variance table.

b. Test the null hypothesis that the population mean yields are identical for all four varieties of corn.

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