Question

1. john scored 85, 88, 92, and 90 on his first four science quizzes. what score does john need to get on his fifth quiz to have an average of exactly 89 on his science quizzes? 90 84 88 96

Explanation:

Step1: Recall average formula

The formula for the average (arithmetic - mean) of a set of numbers is $\text{Average}=\frac{\text{Sum of numbers}}{\text{Number of numbers}}$. Let the score on the fifth quiz be $x$. The sum of the first four scores is $85 + 88+92 + 90=355$, and the number of scores when including the fifth one is $n = 5$, and the desired average is $89$.

Step2: Set up the equation

Using the average formula, we have $89=\frac{355 + x}{5}$.

Step3: Solve the equation for $x$

Multiply both sides of the equation by $5$: $89\times5=355 + x$. So, $445=355 + x$. Then subtract $355$ from both sides: $x=445 - 355$.

Answer:

$90$