SOLUTION: SGT Patrick missed four problems on his math midterm and received a score of 80%. How many problems were on the test?

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Question 1009971: SGT Patrick missed four problems on his math midterm and received a score of 80%. How many problems were on the test?
Found 2 solutions by Theo, Edwin McCravy:
Answer by Theo(13342) About Me  (Show Source):
You can put this solution on YOUR website!
x = number of problems on the test.

4 problems wrong means x-4 problems right.

(x-4)/x = .8

multiply both sides of this equation by x to get x-4 = .8x.

subtract .8x from both sides of this equation and add 4 to both sides of this equation to get x - .8x = 4

combine like terms to get .2x = 4

divide both sides of this equation by .2 to get x = 4/.2 = 20.

there were 20 problems on the test.

he mised 4 so he got 16 right.

16/20 = 8/10 = .8 * 100 = 80%

you could also have just figured out that if he got 80% right, then he must have gotten 20% wrong.

20% wrong = 4

x = total on test.

.20 * x = 4

divide both sides by .20 and you get x = 4/.2 = 20.


Answer by Edwin McCravy(20060) About Me  (Show Source):
You can put this solution on YOUR website!
%28N-4%29%2FN=0.80, Solve for N