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?

Algebra ->  Average -> 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?       Log On


   

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) About Me  (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
%28X%2B80%2B87%29%2F3=84


%28X%2B80%2B87%29=%2884%2A3%29 Multiply both sides by 3 to cancel the denominator for first expression.
%28X%2B80%2B87%29=252
X=85

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) About Me  (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.