John has grades of 82 and 98 on his first two history tests. What must he score on his third test so that his average is at least 88 ?

John's average on all three tests, assuming a score of S on the third test, would be

(82 + 98 + S) / 3

He wants the average to be at least 88, so solve the inequality:

(82 + 98 + S) / 3 ≥ 88

82 + 98 + S ≥ 264

180 + S ≥ 264

S ≥ 84

So John needs to obtain a grade of at least 84 on the third test to get the average he wants.