Skylars grades on four math tests are 85,78,77 and 69 what does skylar need to. score on the next test in order to have a mean score of 80

Skylar's scores in relation to the desired mean are
  +5, -2, -3, -11
for a total of -11.

In order to achieve the desired mean, Skylar must score 11 more than the desired mean: 80 +11 = 91

Skylar needs to score 91 on the next test to have a mean score of 80.

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