SOLUTION: How much distilled water must be mixed with alcohol 70% to prepare 5 L of alcohol 40%?

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Question 714223: How much distilled water must be mixed with alcohol 70% to prepare 5 L of alcohol 40%?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +w+ = liters of distilled water to be used
Let +x+ = liters of 70% alcohol to be used
+.7x+ = liters of alcohol in 70% solution
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I end up with 5 liters, so
(1) +w+%2B+x+=+5+
and also,
(2) ++.7x+%2F+5+=+.4+
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(2) +.7x+=+2+
(2) +x+=+2.8571+
and, since
(1) +w+%2B+x+=+5+
(1) +w+%2B+2.8571+=+5+
(1) +w+=+2.1429+
2.1429 liters of water must be used