SOLUTION: How many liters of pure acid must be mixed with 20 liters of a 15% solution to get a 20% mixture?

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Question 125535: How many liters of pure acid must be mixed with 20 liters of a 15% solution to get a 20% mixture?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
(liters of acid) / (liters of solution) = .20
Let x = liters of pure acid to be added
%28x+%2B+.15%2A20%29+%2F+%28x+%2B+20%29+=+.2
x+%2B+.15%2A20+=+.2%28x+%2B+20%29
x+%2B+3+=+.2x+%2B+4
.8x+=+1
x+=+1.25
1.25 liters of pure acid must be added
check:
%28x+%2B+.15%2A20%29+%2F+%28x+%2B+20%29+=+.2
%281.25+%2B+.15%2A20%29+%2F+%281.25+%2B+20%29+=+.2
%281.25+%2B+3%29+%2F+21.25+=+.2
4.25+%2F+21.25+=+.2
.2+=+.2
OK