SOLUTION: sophie's average mark on 3 tests was 80.the mark on the first test was 76. her average for the first two tests was 18 more than the mark on the third test. what marks did she get o

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Question 587348: sophie's average mark on 3 tests was 80.the mark on the first test was 76. her average for the first two tests was 18 more than the mark on the third test. what marks did she get on the second and third tests?
Answer by lwsshak3(11628) About Me  (Show Source):
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sophie's average mark on 3 tests was 80.the mark on the first test was 76. her average for the first two tests was 18 more than the mark on the third test. what marks did she get on the second and third tests?
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let x=mark of 2nd test
(76+x)/2+18=mark of 3rd test
..
[76+x+(76+x)/2+18]/3=80 (average mark on 3 tests)
multiply top and bottom of left side by 2
(152+2x+76+x+36)/6=80
264+3x=480
3x=216
x=72
(76+x)/2+18=92
ans:
mark of 2nd test=72
mark of 3rd test=92