From past experience, an instructor believes the average score on a particular exam is 85. A sample of 20 student exam scores from a recent exam follows in the table below. 90 78 82 73 86 73 81 80 80 86 91 81 81 75 70 85 79 80 82 84 (a) What assumptions are necessary and how are they satisfied so you can complete the desired test for part (b)? (b) Is there sufficient evidence to suggest the mean is actually less than 85