Jerry’s average (arithmetic mean) score on the first 3 of 4 tests is 78. If Jerry wants to raise his average by 2 points, what score must he earn on the fourth test?  Answers:
A) 87 B) 89 C) 86 D) 93 E) 95

Rationale: "total score on 3 tests = 78 * 3 = 234 jerry wants the average to be = 80 hence total score on 4 tests should be = 80 * 4 = 320 score required on the fourth test = 320 - 234 = 86 option c"
Answer: C