<PRE><B>Question 213395</B>
    how many gallons of a 5% acid solution must be mixed with 5 gallons of a 10% solution to obtain a 7% solution ?
.
Let x = gallons of 5% acid solution added
then
.05x + .10(5) = .07(x+5)
.05x + .5 = .07x+.35
.5 = .02x+.35
.15 = .02x
.15/.02 = x
7.5 gallons = x
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