SOLUTION: How many liters of pure alcohol must be added to 10 liters of a 70% solution to obtain a 90% solution? I know the answer is 20 liters, but I need help with the equation I would us

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Question 585850: How many liters of pure alcohol must be added to 10 liters of a 70% solution to obtain a 90% solution?
I know the answer is 20 liters, but I need help with the equation I would use to figure this out on my own please.

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
+.7%2A10+=+7+ liters of alcohol in 70% solution
In words:
( liters of alcohol you end up with ) / ( total liters of solution ) = 90%
+%28+x+%2B+7+%29+%2F+%28+10+%2B+x+%29+=+.9+
+x+%2B+7+=+.9%2A%28+10+%2B+x+%29+
+x+%2B+7+=+9+%2B+.9x+
+.1x+=+2+
+x+=+2%2F.1+
+x+=+20+
20 liters of pure alcohol must be added