SOLUTION: How many liters of pure alcohol must be added to 15 Liters of a 40% solution to obtain a 70% solution?

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Question 892601: How many liters of pure alcohol must be added to 15 Liters of a 40% solution to obtain a 70% solution?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +x+ = liters of pure alcohol to be added
+.4%2A15+=+6+ liters of alcohol in 40% solution
------------------
+%28+x+%2B+6+%29+%2F+%28+x+%2B+15+%29+=+.7+
+x+%2B+6+=+.7%2A%28+x+%2B+15+%29+
+x+%2B+6+=+.7x+%2B+10.5+
+.3x+=+4.5+
+x+=+15+
15 liters of pure alcohol must be added
check:
+%28+x+%2B+6+%29+%2F+%28+x+%2B+15+%29+=+.7+
+%28+15+%2B+6+%29+%2F+%28+15+%2B+15+%29+=+.7+
+21%2F30+=+.7+
+21+=+.7%2A30+
+21+=+21+
OK