SOLUTION: How much pure acid should be mixed with 5 gallons of a 40% acid solution in order to get a 90% acid solution

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Question 857336: How much pure acid should be mixed with 5 gallons of a 40% acid solution in order to get a 90% acid solution
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +x+ = gallons of pure acid to be added
+.4%2A5+=+2+ = gallons of pure acid in 40% solution
-----------------
+%28+x+%2B+2+%29+%2F+%28+x+%2B+5+%29+=+.9+
+x+%2B+2+=+.9%2A%28+x+%2B+5+%29+
+x+%2B+2+=+.9x+%2B+4.5+
+.1x+=+2.5+
+x+=+25+
25 gallons of pure acid must be added
check:
+%28+x+%2B+2+%29+%2F+%28+x+%2B+5+%29+=+.9+
+%28+25+%2B+2+%29+%2F+%28+25+%2B+5+%29+=+.9+
+27+%2F+30+=+.9+
+9%2F10+=+.9+
OK