SOLUTION: How much pure alcohol must be added to a 4L of a 10% alcohol solution that is 20% alcohol? Please show work not just the answer.

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Question 920233: How much pure alcohol must be added to a 4L of a 10% alcohol solution that is 20% alcohol? Please show work not just the answer.
Found 2 solutions by Alan3354, josmiceli:
Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
Not clear.
4L of a 10% alcohol solution that is 20% alcohol
Is it 10% or 20%?
What do you want to do?

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
+.1%2A4+=+.4+ L of alcohol in 10% solution
Let +x+ = L of pure alcohol to be added
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+%28+.4+%2B+x+%29+%2F+%28+4+%2B+x+%29+=+.2+
+.4+%2B+x+=+.2%2A%28+4+%2B+x+%29+
+.4+%2B+x+=+.8+%2B+.2x+
+.8x+=.4+
+x+=+.5+
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.5 L must be added to the 10% solution
check:
+%28+.4+%2B+x+%29+%2F+%28+4+%2B+x+%29+=+.2+
+%28+.4+%2B+.5+%29+%2F+%28+4+%2B+.5+%29+=+.2+
+.9+%2F+4.5+=+.2+
+.9+=+.9+
OK