SOLUTION: Gina earns score of 65,78,85, and 82 on four tests. What grade must she earn on the next to have an average of 80?

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Question 587371: Gina earns score of 65,78,85, and 82 on four tests. What grade must she earn on the next to have an average of 80?
Found 3 solutions by solver91311, josmiceli, abush:
Answer by solver91311(24713) About Me  (Show Source):
You can put this solution on YOUR website!


If you must have an average of on tests, then the sum of the scores on tests must be . Then, if you already know the scores on of the tests, add those scores and subtract from . The result will be the score necessary to achieve the desired average.

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Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +x+ = her grade on the next test
From the definition of an average:
+%28+65+%2B+78+%2B+85+%2B+82+%2B+x+%29+%2F+5+=+80+
+%28+310+%2B+x+%29+%2F+5+=+80+
+310+%2B+x+=+400+
+x+=+90+
She needs a 90 on the next test to average 80

Answer by abush(5) About Me  (Show Source):
You can put this solution on YOUR website!
(65+78+85+82+n)/5=80
(310+n)/5= 80, multiply both sides by 5
310+n= 400, subtract 310
n=90