SOLUTION: How much water must be mixed with 5 pints of a solution that is 90% developer to produce mixture that is 13% developer

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Question 937551: How much water must be mixed with 5 pints of a solution that is 90% developer to produce mixture that is 13% developer
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +w+ = pints of water needed
+.9%2A5+=+4.5+ pints of developer in 90% solution
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+4.5+%2F+%28+w+%2B+5+%29+=+.13+
+4.5+=+.13%2A%28+w+%2B+5+%29+
+4.5+=+.13w+%2B+.65+
+.13w+=+3.85+
+w+=+29.615+
29.615 pints of water should be added
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check:
+4.5+%2F+%28+w+%2B+5+%29+=+.13+
+4.5+%2F+%28+29.615+%2B+5+%29+=+.13+
+4.5+=+.13%2A34.615+
+4.5+=+4.49995+
close enough