SOLUTION: If Katie scores an 80,83 and an 88 on her first 3 tests, what must she score in her fourth test if she wants an average of 85?

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Question 1142779: If Katie scores an 80,83 and an 88 on her first 3 tests, what must she score in her fourth test if she wants an average of 85?
Found 2 solutions by ikleyn, greenestamps:
Answer by ikleyn(52781) About Me  (Show Source):
You can put this solution on YOUR website!
.

%28%2880%2B83%2B88%29%2Bx%29%2F%283%2B1%29 = 85



80 + 83 + 88 + x = 4*85


x = 4*85 - 80 - 83 - 88 = 89.      ANSWER


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 numbers that are "close together", it is often easy to solve the problem by comparing each individual number to the average.

In this problem, the desired average is 85; the given scores are 80, 83, and 88.

80 compared to the desired average is -5; 83 is -2; 88 is +3.

All together the three tests compared to the average are (-5)+(-2)+(+3) = -4.

So to get the desired average the next test must be +4.

ANSWER: 85+4 = 89