SOLUTION: How much water should be added to 20mL of 12% alcohol solution to reduce the concentration to 10%?

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Question 706361: How much water should be added to 20mL of 12% alcohol solution to reduce the concentration to 10%?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +w+ = mL of water to be added
+.12%2A20+=+2.4+ mL of alcohol in 12% solution
---------------
+2.4+%2F+%28+20+%2B+w+%29+=+.1+
+2.4+=+.1%2A%28+20+%2B+w+%29+
+2.4+=+2+%2B+.1w+
+.1w+=+.4+
+w+=+4+
4 mL of water must be added
check:
+2.4+%2F+%28+20+%2B+4+%29+=+.1+
+2.4+%2F+24+=+.1+
+2.4+=+.1%2A24+
+2.4+=+2.4+
OK