4. [22 marks] a) In an agricultural experiment, three blocks of similar size and location have been selected. On each block, four varieties (A, B, C and D) of potatoes have been grown on plots of equal size. The yields of potato from the 12 plots have been registered in the table below: Variety A Variety B Variety C Variety D Block 1 68 67 71 77 Block 2 82 83 86 89 Block 3 56 59 64 60 Analyze these data using the Friedman test. At 10% level of significance, decide if the hypothesis of equal yields for the four varieties can be ac- cepted.b) Two groups of students attempt a test with the following results: Group 1: 91, 83, 76, 81 Group 2: 72, 61, 74, 63, 82 Using a (large sample) Wilcoxon test and a = 0.05, test the hypothesis of no difference between the two groups