Four sections of the same statistics course are taught by four teachers. Using the data given below and a level of significance of 5%, are the average grades of the four classes significantly different?

Class 1 78 83 65 74 91 83 — —

Class 2 92 81 87 76 94 85 90 —

Class 3 63 71 65 68 83 — — —

Class 4 94 87 89 92 90 89 85 93