SOLUTION: A contractor mixes concrete from bags of pre-mix for small jobs. How many bags with 3% cement should he mix with 10 bags of 18.2% cement to produce a mix containing 11% cement?

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Question 1025511: A contractor mixes concrete from bags of pre-mix for small jobs. How many bags with 3% cement should he mix with 10 bags of 18.2% cement to produce a mix containing 11% cement?
Found 2 solutions by fractalier, josmiceli:
Answer by fractalier(6550) About Me  (Show Source):
You can put this solution on YOUR website!
Call the number of bags of 3% cement, x. Then the setup looks like this:
.03x + .182(10) = .11(10+x)
Now solve for x.
.03x + 1.82 = 1.1 + .11x
.72 = .08x
x = 9 bags of 3% cement

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +x+ = bags of 3% cement needed
+.182%2A10+=+1.82+ bags of pure cement in 18.2% mix
--------------------
+%28+.03x+%2B+1.82+%29+%2F+%28+x+%2B+10+%29+=+.11+
+.03x+%2B+1.82+=+.11%2A%28+x+%2B+10+%29+
+.03x+%2B+1.82+=+.11x+%2B+1.1+
+.08x+=+.72+
+x+=+9+
9 bags of 3% cement are needed
-------------
check:
+%28+.03x+%2B+1.82+%29+%2F+%28+x+%2B+10+%29+=+.11+
+%28+.03%2A9+%2B+1.82+%29+%2F+%28+9+%2B+10+%29+=+.11+
+%28+.27+%2B+1.82+%29+%2F+19+=+.11+
+.27+%2B+1.82+=+2.09+
+2.09+=+2.09+
OK