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

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) (Show Source): You can put this solution on YOUR website!

let her fourth test score be
if she wants an average of , than

her fourth test score should be

Answer by greenestamps(13200) (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

RELATED QUESTIONS
If Katie scores an 80,83 and an 88 on her first 3 tests, what must she score in her... (answered by ikleyn,greenestamps)
If Sarah scored an 80,95,75 and an 90 on her first four test , what must she score on her (answered by ikleyn,greenestamps)
Jackie has grades of 83, 76, and 65 on her first three algebra tests. If she wants an... (answered by Fombitz)
Alissa has test grades of 90, 87, and 79 on her first three algebra tests. If she wants... (answered by nerdybill)
Melinda scored 84%, 75% and 77% on her first three tests of the term. What score will she (answered by Boreal,ewatrrr)
jon wants an average test score of 88. if he scored 74, 92, and 84 on the first three... (answered by CubeyThePenguin)
Shania has scores of 76 and 81 on her first two tests. If she wants an average of at... (answered by solver91311)
Sarah has grade of 99 and 69 on her first two tests. If she wants an average of at least... (answered by checkley77)
Susan Jacobson has grades of 76 and 81 on her first two algebra tests. If she wants an... (answered by KMST)