# If you scored a 82, 92, and 87 on the first three chapter tests, what do you need to score on the fourth test to get an average test score of 91%?

Mar 24, 2018

You would have to score a $103$

#### Explanation:

The formula for finding an average is to add all of the scores together, and then divide by the number of scores. Since we do not know one of the scores, I will call it $x$. We do, however know the average, so we can make this equation:

$\frac{82 + 92 + 87 + x}{4} = 91$

Multiply $4$ to both sides to remove the division. Then solve:

$\frac{82 + 92 + 87 + x}{\cancel{4}} \times \cancel{\textcolor{b l u e}{4}} = 91 \times \textcolor{b l u e}{4}$

$82 + 92 + 87 + x = 364$

$174 + 87 + x = 364$

$261 + x = 364$

$x = 103$

You would have to score a $103$ to bring your average up to 91%.