After five tests, Mike's average score is 91. After 6 tests, his average score was 89. what was his score, on the sixth test?

(x 1 + x 2 + x 3 + x 4 + x 5) / 5 = 89 Multiply both sides by 5

x 1 + x 2 + x 3 + x 4 + x 5 = 89 * 5 = 445

(x 1 + x 2 + x 3 + x 4 + x 5 + x 6) / 6 = 90

(445 + x 6) / 6 = 90 Multiply both sides by 6

445 + x 6 = 6 * 90 = 540

x 6 = 540 - 445 = 95