SOLUTION: how many gallons of 40% salt solution must be mixed with 8 gallons of a 10% solution to make a 30% mixture solution?

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Question 1060804: how many gallons of 40% salt solution must be mixed with 8 gallons of a 10% solution to make a 30% mixture solution?
Found 2 solutions by Boreal, josgarithmetic:
Answer by Boreal(15235) About Me  (Show Source):
You can put this solution on YOUR website!
x=gallons
.40x+8(.10)=(x+8)(.30)
.40x+0.8+.30x+2.4
.10x=1.6
x=16 gallons.
That is a 2:1 ratio, and 30% is twice as far from 10% as it is from 40% to check.

Answer by josgarithmetic(39620) About Me  (Show Source):
You can put this solution on YOUR website!
40% salt solution is a suspiciously unrealistic concentration, but here is working with just the algebra, ignoring that:

x, how many gallons of the "40% salt solution" to add

EQUATION TO BEGIN:
%2840x%2B10%2A8%29%2F%28x%2B8%29=30


40x%2B10%2A8=30%28x%2B8%29
4x%2B8=3%28x%2B8%29
4x%2B8=3x%2B24
x%2B8=24
x=16