SOLUTION: how to compute the next grade if the average is given? ex. average= 90 scored= 86+92+89+88+?

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Question 659111: how to compute the next grade if the average is given?
ex.
average= 90
scored= 86+92+89+88+?
Answer by colliefan(242) About Me  (Show Source):
You can put this solution on YOUR website!
Write what you know as the equation that would be used to calculate an average and then solve for the unknown.
Avg=%2886%2B92%2B89%2B88%2Bx%29%2F5
90=%2886%2B92%2B89%2B88%2Bx%29%2F5
90%2A5=%28%2886%2B92%2B89%2B88%2Bx%29%2F5%29%2A5
450=%28%2886%2B92%2B89%2B88%2Bx%29
450=355%2Bx
450-355=355%2Bx-355
95=x