Peter's average (arithmetic mean) test score on 4 tests is 78. What must be the student's score on a 5th test for the Peter's average score on the 5 tests to be 80? Pick:
A) 80  B) 82  C) 84  D) 86  E) 88

Rationale: e . 88 peter must score at least an 80 for sure . if he scores an 8 , then he will need to score 2 pots for each of the 4 other tests tomake upthe difference . they each were at 78 ( at least the average is , but this is a small point and does n ' t matter to the answer ) . so 4 tests that were each 2 points short of the 80 average that is desired means the next test must be 8 points higher than the desired average , so 80 + 8 = 88 .
Answer: E