SOLUTION: A mixture containing 10% salt is to be mixed with 4 ounces of a mixture that is 20% salt, in order to obtain a 15% solution that is salt. How much of the first solution must be us

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Question 757130: A mixture containing 10% salt is to be mixed with 4 ounces of a mixture that is 20% salt, in order to obtain a 15% solution that is salt. How much of the first solution must be used?
Answer by josgarithmetic(39617) About Me  (Show Source):
You can put this solution on YOUR website!
The description seems to deal with "masses".
Let m= ounces of the 10% solution to use.

%2810m%2B20%2A4%29%2F%28m%2B4%29=15
And you know from the numbers given that m must be exactly 4 ounces, because you would want equal amounts of the 10% and the 20% to achieve the 15%, exactly in the middle of the two available solutions.

That above is the equation. Solve for m.
10m%2B20%2A4=15%28m%2B4%29
2m%2B16=3%28m%2B4%29
2m%2B16=3m%2B12
16=m%2B12
16-12=m
m=4