SOLUTION: Please help. A contractor mixes concrete from bags of pre-mix for small jobs. How many bags with 7% cement should he mix with 10 bags of 15.5% cement to produce a mix containing

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Question 278856: Please help.
A contractor mixes concrete from bags of pre-mix for small jobs. How many bags with 7% cement should he mix with 10 bags of 15.5% cement to produce a mix containing 12% cement?
Answer by richwmiller(17219) About Me  (Show Source):
You can put this solution on YOUR website!
.07*x+10*.155=(10+x)*.12
x=7 bags to add for a total mix of 17 bags