SOLUTION: how many litres of 50% alchol solution must be mixed with 90 liters of 80% solution to get a 70% soulton

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Question 997875: how many litres of 50% alchol solution must be mixed with 90 liters of 80% solution to get a 70% soulton
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +x+ = liters of 50% alcohol needed
+.5x+ = liters of alcohol in 50% solution
+.8%2A90+=+72+ liters of alcohol in 80% solution
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+%28+.5x+%2B+72+%29+%2F+%28+x+%2B+90+%29+=+.7+
+.5x+%2B+72+=+.7%2A%28+x+%2B+90+%29+
+.5x+%2B+72+=+.7x+%2B+63+
+.2x+=+9+
+x+=+45+
45 liters of 50% alcohol are needed
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check:
+%28+.5x+%2B+72+%29+%2F+%28+x+%2B+90+%29+=+.7+
+%28+.5%2A45+%2B+72+%29+%2F+%28+45+%2B+90+%29+=+.7+
+%28+22.5+%2B+72+%29+%2F+135+=+.7+
+94.5+=+.7%2A135+
+94.5+=+94.5+
OK