SOLUTION: How do I show my work for this problem? I know the answer, I just don't understand how to get it, please help! Zach took four biology tests and got scores of 83, 86, 91, and 77.

Question 872590: How do I show my work for this problem? I know the answer, I just don't understand how to get it, please help!
Zach took four biology tests and got scores of 83, 86, 91, and 77. He needs to complete one more test. If he wants to get an average of 85 on all five tests, what score does he need on his last test?
Answer by jim_thompson5910(35256) (Show Source): You can put this solution on YOUR website!
Let x = score on the fifth test

The scores for the five tests are: 83, 86, 91, 77, x

They add to 83+86+91+77+x = 337+x

Divide that sum by 5 to get the average. We want this average to be equal to 85. Set it equal to 85 and solve for x.

(337+x)/5 = 85
337+x = 85*5
337+x = 425
x = 425-337
x = 88

He needs to get an 88 on the last test.
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