Question 1195114
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When working a problem like this involving the average of a set of numbers that are all close together, you can keep the numbers in your calculations smaller by comparing the individual values to the average.  Compared to the desired average of 85....<br>
80 is 5 points below: -5
83 is 2 points below: -2
88 is 3 points above: +3<br>
Compared to the desired average, the first three scores together are 4 points below the average: (-5)+(-2)+(+3) = -4<br>
That means her score on the 4th test must be 4 points above the desired average.<br>
ANSWER: 85+4 = 89<br>