Kelly's scores on the first three tests in her physics class are 79, 84, and 68. Determine all scores on the fourth test that will yield an average test score of at least 80.

Answer 1

(x + 79 + 84 + 68)/4 = 80
(x + 231)/4 =80
x +231 = 320
x + 231- 231 = 320-231
x = 89
Fourth test 89