During a math course a student takes 8 tests. All of these test are of equal value. When figuring out the final grade, the instructor drops the best and the worst grades and averages the other six. The student calculates that his average for all eight tests is 84%. After dropping the best and the worst grades the student averages 86%. What was the average of the best adn the worst test?
A. 68
B. 72
C. 78
D. 88
E. This cannot be determined with the amount of information provided.
If the average for the eight tests is 84%, then the sum of the eight tests must be 8 times 84 or 672. For the six tests the sum must be 6 times 86 or 516. The two dropped tests must have accounted for 156 points.
156 / 2 = 78.