SOLUTION: How much water must be evaporated from 32oz of a 4% solution to make a 6% salt solution?

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Question 489801: How much water must be evaporated from 32oz of a 4% solution to make a 6% salt solution?
Found 2 solutions by chessace, josmiceli:
Answer by chessace(471) About Me  (Show Source):
You can put this solution on YOUR website!
As usual, ans = x = H2O to go into thick air.
Salt is same quant before and after: 0.06 * (32 -x) = 0.04 * 32
*100, subtract righhand side:
6*32 -6x = 4*32
6x = (6-4)*32
x = 32/3
Taking away a third is exactly what you would expect: The remaining thirds have to split the extra 4% salt 2 ways, 4 + 4/2 = 6.

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
The key is that you have as much salt after evaporation as before
In words:
(ounces of salt)/(total salt + water solution at end) = 6%
given:
+.04%2A32+=+1.28+ ounces of salt at start
+32+-+1.28+=+30.72+ ounces of water at start
-------------------
Let +w+ = ounces of water to be evaporated
+1.28+%2F+%2832+-+w%29+=+.06+
+1.28+=+.06%2A%2832+-+w%29+
+1.28+=+1.92+-+.06w+
+.06w+=+1.92+-+1.28+
+.06w+=+.64+
+w+=+10.667+
10.667 ounces of water must be evaporated
check:
That leaves +30.72+-+10.667+=+20.053+ ounces of water
+1.28+%2F+%28+20.053+%2B+1.28+%29+=+1.28+%2F+21.333+
+1.28+%2F+21.333+=+.06000+
OK