SOLUTION: The average mark for 100 learners in a test is 39%. The average mark for the learners who passed is 60%, while the average mark for the learners who failed is 30%.

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Question 1025086: The average mark for 100 learners in a test is 39%. The average mark for the learners who passed is 60%, while the average mark for the learners who failed is 30%. Compute the number of learners who failed the test
Answer by robertb(5830) About Me  (Show Source):
You can put this solution on YOUR website!
Let S%5Bp%5D+ = sum of averages of the passes, and S%5Bf%5D+ = sum of the averages of the failures.
==> %28S%5Bp%5D%2BS%5Bf%5D%29%2F100+=+0.39 ==> S%5Bp%5D%2BS%5Bf%5D=+39.
Let x = number of passes, so that 100 - x = number of failures.
==> S%5Bp%5D%2Fx+=+0.60 and S%5Bf%5D%2F%28100+-+x%29+=+0.30
==> S%5Bp%5D=+0.60x and S%5Bf%5D=0.30%28100+-+x%29
==> S%5Bp%5D+%2B+S%5Bf%5D=+0.60x+%2B+0.30%28100+-+x%29+=+39 ==> x = 30, the number of passes, and
100 - x = 70, the number of failures.