SOLUTION: how many liters of pure acid must grace add to four liters of a 10% acid solution to increase the strength to 80%

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Question 567250: how many liters of pure acid must grace add to four liters of a 10% acid solution to increase the strength to 80%
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +x+ = liters of pure acid to be added
+.1%2A4+=+.4+ liters of acid in 10% solution
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+%28+x+%2B+.4+%29+%2F+%28+x+%2B+4+%29+=+.8+
+x+%2B+.4+=+.8%2A%28+x+%2B+4+%29+
+x+%2B+.4+=+.8x+%2B+3.2+
+.2x+=+3.2+-+.4+
+.2x+=+2.8+
+x+=+14+
14 liters of pure acid is needed
check:
+%28+x+%2B+.4+%29+%2F+%28+x+%2B+4+%29+=+.8+
+%28+14+%2B+.4+%29+%2F+%28+14+%2B+4+%29+=+.8+
+14.4+%2F+18+=+.8+
+14.4+=+.8%2A18+
+14.4+=+14.4+
OK