Question

A student scored 75 and 97 on her first two quizzes. Write and solve a compound inequality to find the possible values for a third quiz score that would give her an average between 85 and 90, inclusive.

Answer 1

Answer:

$85 \le \frac{75 + 97 + n}{3} \le 90$; $83 \le n \le 98$

Step-by-step explanation:

Score of the first two quizzes: 75 and 97

Let n represent the third score

Average score would be: $\frac{75 + 97 + n}{3}$.

Given that the average score fall between 85 and 90, this can be represented by the compound inequality as shown below:

$85 \le \frac{75 + 97 + n}{3} \le 90$

Solve for n in each statement that makes up the compound inequality:

$85 \le \frac{75 + 97 + n}{3}$

$85 \le \frac{172 + n}{3}$

Multiply both sides by 3

$85*3 \le 172 + n$

$255 \le 172 + n$

Subtract 172 from each side of the inequality

$255 - 172 \le n$

$83 \le n$

Also,

$\frac{75 + 97 + n}{3} \le 90$

$\frac{172 + n}{3} \le 90$

Multiply both sides by 3

$172 + n \le 90*3$

$172 + n \le 270$

Subtract 172 from both sides of the inequality

$n \le 270 - 172$

$n \le 98$

Combining both together, the possible values of her third quiz score would be:

$83 \le n \le 98$