SOLUTION: How many gallons of a 12%-salt solution must be mixed with 6 gallons of a 20%-salt solution to obtain a 15%-salt solution?

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Question 885664: How many gallons of a 12%-salt solution must be mixed with 6 gallons of a 20%-salt solution to obtain a 15%-salt solution?
Answer by Theo(13342) About Me  (Show Source):
You can put this solution on YOUR website!
.12x + .2*6 = .15*(x+6)
simplify to get:
.12x + 1.2 = .15x + .9
subtract .9 from both sides of the equation and subtract .12x from both sides of the equation to get:
1.2 - .9 = .15x - .12x
simplify to get:
.3 = -.03x
divide both sides of this equation by -.03 to get:
x = 10
that should be your answer.
replace x in your original equation with 10 to see if that's right.
.12x + .2*6 = .15*(x+6) becomes:
.12*10 + .2*6 = .15*16
simplify this to get:
1.2 + 1.2 = 1.5 + .9
simplify further by combining like terms to get:
2.4 = 2.4
this is correct so the answer is good.
10 gallons of a 12% salt solution must be mixed with 6 gallons of a 20% salt solution to get 16 gallons of a 15% solution.