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

He currently has 309 points in total. To have a mean of 80 after 5 tests, the total has to be 400, since 400 = 80*5.

400-309 = 91

So Skylar needs 91 points.

Answer 2

Answer:  The correct option is (c) 91.

Step-by-step explanation:  Given that Skylar's grades on four math tests are 85, 78, 77, and 69.

We are to find the grades that Skylar need to score on the next test in order to have a mean score of 80.

Let x denote the grades that Skylar need to score on the next test in order to have a mean score of 80.

Then, according to the given information, we have

$\textup{Mean of 5 tests}=80\\\\\\\Rightarrow \dfrac{85+78+77+69+x}{5}=80\\\\\\\Rightarrow \dfrac{309+x}{5}=80\\\\\Rightarrow 309+x=400\\\\\Rightarrow x=400-309\\\\\Rightarrow x=91.$

Thus, Skylar need to score 91 grades in the next test.

Option (c) is CORRECT.