SOLUTION: How much water must be evaporated from 30 gallons of a 7% salt solution to make a 12% salt solution?

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Question 990669: How much water must be evaporated from 30 gallons of a 7% salt solution to make a 12% salt solution?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +x+ = gallons of water to be evaporated
You start with +.07%2A30+=+2.1+ gallons of salt
and you end up with the same amount
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+2.1+%2F+%28+30+-+x+%29+=+.12+
+2.1+=+.12%2A%28+30+-+x+%29+
+2.1+=+3.6+-+.12x+
+.12x+=+3.6+-+2.1+
+.12x+=+1.5+
+x+=+12.5+
12.5 gallons should be evaporated
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check:
+2.1+%2F+%28+30+-+x+%29+=+.12+
+2.1+%2F+%28+30+-+12.5+%29+=+.12+
+2.1+%2F+17.5+=+.12+
+2.1+=+.12%2A17.5+
+2.1+=+2.1+
OK