Question

Skylar's 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? A) 83. B) 90. C) 91

Answer 1

If Skylar's grades on four of her math tests are 85, 78, 77, and 69, she must score a 90 on the next text in order to have her mean score of 80. The answer will be A. 

Answer 2

(85 + 78 + 77 + 69 + x) / 5 = 80
(309 + x)/5 = 80
309 + x = 80 * 5
309 + x = 400
x = 400 - 309
x = 91 <== skylar needs to score a 91 to have an average of 80