SOLUTION: If Katie scored an 80, 83, and an 88 on her first three tests, what must she score on her fourth test if she wants an average of 85? Enter your answer in the text box below

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Question 1195114: If Katie scored an 80, 83, and an 88 on her first
three tests, what must she score on her fourth
test if she wants an average of 85? Enter your
answer in the text box below
Found 2 solutions by MathLover1, greenestamps:
Answer by MathLover1(20849) About Me  (Show Source):
You can put this solution on YOUR website!


let her fourth test score be x
if she wants an average of 85, than
%2880%2B83%2B88%2Bx%29%2F4=85
80%2B83%2B88%2Bx=4%2A85
251%2Bx=340
x=340-251
x=89

her fourth test score should be 89


Answer by greenestamps(13200) About Me  (Show Source):
You can put this solution on YOUR website!


When working a problem like this involving the average of a set of numbers that are all close together, you can keep the numbers in your calculations smaller by comparing the individual values to the average. Compared to the desired average of 85....

80 is 5 points below: -5
83 is 2 points below: -2
88 is 3 points above: +3

Compared to the desired average, the first three scores together are 4 points below the average: (-5)+(-2)+(+3) = -4

That means her score on the 4th test must be 4 points above the desired average.

ANSWER: 85+4 = 89