SOLUTION: Hi, I'm in Algebra 2. And ever since I was little I always had problems with story problems. If someone can help me with this problem it would be greatly appreciated! The story

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Question 775499: Hi, I'm in Algebra 2. And ever since I was little I always had problems with story problems. If someone can help me with this problem it would be greatly appreciated!
The story problems starts as "Mary has grades of 98, 76, 86, and 92 on four tests. Within what range must her grade on a fifth test fall if she wishes an average between 80 and 90 on all five tests?"
I've tried to come up with an equation but I come up with none. I've asked my parents but they were left dumbfounded like me. Again I would appreciate all the help I could get! Thank you!

Answer by reviewermath(1029) About Me  (Show Source):
You can put this solution on YOUR website!
Q:
Mary has grades of 98, 76, 86, and 92 on four tests. Within what range must her grade on a fifth test fall if she wishes an average between 80 and 90 on all five tests?
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A:
Let x = Mary's grade on fifth test
Average = %2898+%2B+76+%2B+86+%2B+92+%2B+x%29%2F5 = %28362+%2B+x%29%2F5.
80+%3C=+%28352%2Bx%29%2F5+%3C=+90, multiply both sides by 5
400+%3C=+352%2Bx+%3C=+450, subtract both sides by 352
400-352+%3C=+x+%3C=+450-352
48+%3C=+x+%3C=+98
Answer: between 48 and 98