SOLUTION: how many gallons of hydrochloric acid must be added to 12 gallons of a 30% solution to obtain a 40% solution?

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Question 275647: how many gallons of hydrochloric acid must be added to 12 gallons of a 30% solution to obtain a 40% solution?
Answer by checkley77(12844) About Me  (Show Source):
You can put this solution on YOUR website!
.30*12+x=.40(12+x)
3.6+x=4.8+.40x
x-.40x=4.8-3.6
.6x=1.2
x=1.2/.6
x=2 gallons of acid needs to be added.
Proof:
.30*12+2=.4(12+2)
3.6+2=.4*14
5.6=5.6