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