Question 380610
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Hi,
Let x represent the amount of the 100% pure acid solution
1.00x + .10*6gal = .90*(x + 6gal)
solving for x
.10x = .80*6gal
x = 48 gal of pure acid needed.

CHECKING our Answer
48gal + .6gal = 48.6gal = .9*54gal = 48.6gal