Astudent scored 83 and 91 on their first two quizzes. write and solve a compound inequality to find the possible values for a third quiz score that would give them an average between 85 and 90, inclusive

To find the mean of a data set, we follow the following formula

Mean = sum of values in data set ÷ number of values in data set

We have three values in given data set: 83, 91, and an unknown value 

We want to work out a range of possible value of  such as the mean is in between 85 and 90 inclusive

We first set the inequality


, multiply each term by 3 
, subtract 174 from each term
 

So the possible values of x are in between 81 and 96 inclusive