SOLUTION: this question didn't come out of a textbook. It was from a paper in my math class. here it goes. How much pure acid do you add to 2 gallons of 40% acid in order to get a 70% acid.

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Question 97755: this question didn't come out of a textbook. It was from a paper in my math class. here it goes.
How much pure acid do you add to 2 gallons of 40% acid in order to get a 70% acid.
I don't know how to set up the equation to solve it. Can you help?

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
First I ask: how much acid is in the original solution?
It's .4%2A2+=+.8 gallons
Call the gallons of acid you want to add x
%28x+%2B+.8%29+%2F+2+=+.7
x+%2B+.8+=+1.4
x+=+.6
So, you add .6 gallons of acid to get a 70% solution