Question 1208136: If a student scores 85,79,92, and 100 on her math quizzes then what was her average grade?
Found 2 solutions by josgarithmetic, greenestamps:
Answer by josgarithmetic(39620)   (Show Source):
Answer by greenestamps(13200)  (Show Source):
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By the basic method, using the definition of average directly....
ANSWER: 89
Or by a method which is sometimes easier in cases where all the numbers are "close together"....
(1) Using a quick examination of the given numbers, make a guess for the average. In this example, 90 should be close.
(2) Determine, for each given number, the "over" or "under" compared to your guess for the average; then find the total over or under.
85: -5
79: -11
92: +2
100: +10
total: -16+12 = -4
(3) Divide the total over or under by the number of quiz scores to find the average over or under
-4/4 = -1
Adjust your guess by that average over or under to get the actual average
90+(-1) = 89
ANSWER (again, of course): 89
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