SOLUTION: A student has a mean (average) score of 88 in her math class. This is the average of her first five math tests. What must she score on the sixth test in order to have a mean score

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Question 1092009: A student has a mean (average) score of 88 in her math class. This is the average of her first five math tests. What must she score on the sixth test in order to have a mean score of 90?
Found 2 solutions by josmiceli, greenestamps:
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +x+ = her score on the 6th test
Let +S+ = the sum of her first 5 test scores
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+S%2F5+=+88+
+S+=+440+
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Now I can say:
+%28+S+%2B+x+%29+%2F+6+=+90+
+%28+440+%2B+x+%29+%2F+6+=+90+
+440+%2B+x+=+540+
+x+=+100+
She must score 100 on her 6th test in
order to average 90

Answer by greenestamps(13200) About Me  (Show Source):
You can put this solution on YOUR website!

When solving a problem like this involving an average where all the numbers are close together, it is often easiest to compare the existing scores to the desired average.

In your problem, the student has an average of 88 on her first 5 tests, and she wants an average of 90 after the next test. On average, the existing 5 tests are each 2 points below the desired average, so overall she is 10 points short of what she needs to get her desired average. That means she needs to be 10 points above that desired average on the next test. 10 points above the desired average of 90 is 100.

She needs to get 100 on the next test to achieve an average of 90 for all 6 tests.