SOLUTION: how much pure acid must be added to 6 gallons of 4% acid solution to make 20% acid solution? So far I have let x +6 *.04 ?? not sure if this correct

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Question 572476: how much pure acid must be added to 6 gallons of 4% acid solution to make 20% acid solution?
So far I have let x +6 *.04 ?? not sure if this correct

Answer by nerdybill(7384) About Me  (Show Source):
You can put this solution on YOUR website!
how much pure acid must be added to 6 gallons of 4% acid solution to make 20% acid solution?
.
Let x = amount (gallons) of pure acid added
then
"pure acid" + "acid in 4% solution" = 20% of total mixture
x + .04(6) = .20(6+x)
x + .24 = 1.2+.20x
.80x + .24 = 1.2
.80x = 0.96
x = 1.2 gallons