SOLUTION: How many liters of pure alcohol must be added to 5 liters of a 15% alcohol solution to make a 25% solution?

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Question 831330: How many liters of pure alcohol must be added to 5 liters of a 15% alcohol solution to make a 25% solution?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +x+ = liters of pure alcohol needed
+%28+x+%2B+.15%2A5+%29+%2F+%28+x+%2B+5+%29+=+.25+
+x+%2B+.75+=+.25%2A%28+x%2B5+%29+
+x+%2B+.75+=+.25x+%2B+1.25+
+.75x+=+.5+
+x+=+.667+ liters
2/3 of a liter of pure alcohol must be added
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check:
+%28+x+%2B+.15%2A5+%29+%2F+%28+x+%2B+5+%29+=+.25+
+%28+.667+%2B+.15%2A5+%29+%2F+%28+.667+%2B+5+%29+=+.25+
+.667+%2B+.75+=+.25%2A5.667+
+1.417+=+1.4168+
close enough