An experiment was carried out to test the effects on yields of five varieties of corn and five types of fertilizer. For each variety-fertilizer combination, six plots were used and the yields recorded, with the results shown in the following table:

a. Test the null hypothesis that the population mean yields are the same for all five varieties of corn.
b. Test the null hypothesis that the population mean yields are the same for all five brands of fertilizer.
c. Test the null hypothesis of no interaction between variety and fertilizer.

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