The grades received on a test by twenty students were 100, 55, 75, 80, 65, 65, 95, 90, 80, 45, 40, 50, 85, 85, 85, 80, 80, 70, 65, and 60. what is the average of these grades? a.) 70.5 b.) 72.5 c.) 77 d.) 80.3 e.) 100