SOLUTION: A contractor mixes concrete from bags of pre-mix for small jobs. How many bags with 4% cement should he mix with 10 bags of 11.6% cement to produce a mix containing 8% cement?

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Question 112754:
A contractor mixes concrete from bags of pre-mix for small jobs. How many bags with 4% cement should he mix with 10 bags of 11.6% cement to produce a mix containing 8% cement?
Answer by checkley71(8403) About Me  (Show Source):
You can put this solution on YOUR website!
10*.116+.04X=.08(10+X)
1.16+.04X=.8+.08X
.04X-.08X=.8-1.16
-.04X=-.36
X=-.36/-.04
X=9 BAGS OF 4% CEMENT.
PROOF
10*.116+.04*9=.08(10+9)
1.16+.36=.08*19
1.52=1.52