SOLUTION: Sarah has 65 milliliters of a 30% solution. How many millimeters of 75% solution should she add to obtain the required 35% solution?

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Question 1049113: Sarah has 65 milliliters of a 30% solution. How many millimeters of 75% solution should she add to obtain the required 35% solution?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +x+ = ml of the 75% solution needed
+.3%2A65+=+19.5+ = ml of concentrate in the 30% solution
+.75x+ = ml of concentrate in the 75% solution
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+%28+19.5+%2B+.75x+%29+%2F+%28+65+%2B+x+%29+=+.35+
+19.5+%2B+.75x+=+.35%2A%28+65+%2B+x+%29+
+19.5+%2B+.75x+=+22.75+%2B+.35x+
+.4x+=+22.75+-+19.5+
+.4x+=+3.25+
+x+=+8.125+
8.125 ml of the 75% solution is needed
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check answer:
+%28+19.5+%2B+.75x+%29+%2F+%28+65+%2B+x+%29+=+.35+
+%28+19.5+%2B+.75%2A8.125+%29+%2F+%28+65+%2B+8.125+%29+=+.35+
+%28+19.5+%2B+6.09375+%29+%2F+73.125+=+.35+
+25.59375+%2F+73.125+=+.35+
+25.59375+=+.35%2A73.125+
+25.59375+=+25.59375+
OK