$\bar{x}_1 = (72 + 78 + 65 + 74 + 80 + 71 + 76 + 69 + 77 + 73)/10 = 73.5$ - $\bar{x}_2 = (68 + 75 + 71 + 62 + 69 + 74 + 66 + 72 + 67 + 70)/10 = 69.4$ - $\bar{x}_3 = (81 + 85 + 79 + 88 + 83 + 86 + 80 + 90 + 84 + 82)/10 = 83.8$ - $\bar{x}_4 = (55 + 62 + 58 + 51 + 60 + 57 + 63 + 54 + 59 + 56)/10 = 57.5