SOLUTION: The average, or mean, of your last three math tests is 84%. On the first two tests you earned an 80% and an 87%. What did you earn on the third math test?

Question 747823: The average, or mean, of your last three math tests is 84%. On the first two tests you earned an 80% and an 87%. What did you earn on the third math test?
Found 2 solutions by FrankM, Cromlix:
Answer by FrankM(1040) (Show Source): You can put this solution on YOUR website!
To fins the average we add N numbers and divide by N. Here, N =3

Multiply both sides by 3 to cancel the denominator for first expression.

Note - 80 is the average -4, 87 is the average +3. The missing number must be the average +1, so the differences to the average cancel to zero. This is a shortcut that avoids any multiplying, and can help you solve this type of short problem on your fingers.

Answer by Cromlix(4381) (Show Source): You can put this solution on YOUR website!
If a mean of 84% was achieved for three
maths tests then the total marks received for the 3
was 3 x 84 = 252
The total of the first two tests was 167.
252 - 167 = 85. This is what was earned for
the third test.
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