SOLUTION: Marie received the following scores on her first three tests: 91% 87% and 86% What average must she receive on her fourth and fifth test to average 90% for all five tests?

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Question 498430: Marie received the following scores on her first three tests: 91% 87% and 86% What average must she receive on her fourth and fifth test to average 90% for all five tests?
Answer by bucky(2189) (Show Source):
You can put this solution on YOUR website!
To average 90 on 5 tests, it will be necessary for Marie to get a total of 450 points. (450 = 90 * 5 or you can look at it as dividing 450 points by 5 tests results in an average of 90).
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Marie has scored a total of 264 points on the first three tests. (91 + 87 + 86 = 264)
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So on the next two tests Marie must score 186 points (the 450 she needs minus the 264 she has already scored).
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So if she needs 186 points on the two tests remaining she must average 93 points on each of the two tests (186 points divided by two tests = 93).
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Here's another way you can do this problem if you can follow this:
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Marie wants to average 90 on five tests. On the first test she scored one above 90. On a second test she scored three below 90. And on a third test she scored four below 90. So in trying to get a 90 average she is +1 - 3 -4 = -6 points below where she needs to be to average 90. So on the last two tests she needs to make up those six points by scoring above 90. To make up six points on two tests she will have to score an average of 6/2 = 3 points above 90 on each test. So if she scores 93 on each of the two remaining tests, she will have an average of 90 on the five tests.
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Hope this helps you to understand the problem a little better.
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