Question

Malena has taken four tests so far. Her scores are 92%,80%,88%,93%. What score does she need to get on the fifth test to raise her average grade to 90%?

Answer 1

To calculate the average you add up all the scores and divide by the number of scores (5)
add all the current test scores and allow X to be the unknown score:
92+80+88+93+X: or 353 + X

set up equation:

(353+X)
______    =  90
    5

Multiply both side of the equation by 5 to clear the fraction resulting in:

353+X=450

Subtract 353 from both sides of the equation:

x = 97

So the test score needed to get a 90 average is 97.