SOLUTION: An average of 90% is needed on five tests to receive an A in a class. If a student received scores of 95, 85, 88 and 84 on the first four tests, what will the student need to get a

Question 1086897: An average of 90% is needed on five tests to receive an A in a class. If a student received scores of 95, 85, 88 and 84 on the first four tests, what will the student need to get an A.
I found this method of getting the answer, but I want to know what this calculation method is called?
The second column shows how far or over the scores are from the 90% average. If the total is positive then add to the average if it's negative then subtract from average.
95 - 5 less
85 + 5 more
88 + 2 more
84 + 6 more
Since the sum of 2nd column is positive add it to 90 and the answer is 98.

Answer by Boreal(15235) (Show Source): You can put this solution on YOUR website!
That works, and I use it often preferentially. I look at the difference from the average, and the difference is 5 above -13 below or -8. Therefore, the last score has to be 8 above the mean or 98.
I use the concept that the sum of the differences from a mean must equal 0. This usually is discussed in variability, where we square the differences, to make them positive, then add them and divide by N or n-1 to get the variance. The mean deviation is occasionally used, which takes the absolute value of all the differences, again recognizing that the sum of the differences themselves must always equal 0.
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