SOLUTION: If you have 90 ounces of water to make a 10% salt solution, what is the decrease in ounces of water to make a 15% salt solution.

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Question 228905: If you have 90 ounces of water to make a 10% salt solution, what is the decrease in ounces of water to make a 15% salt solution.
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
In words:
(ounces of salt in final solution)/(water + salt in final solution) = 15%
Let a = ounces of salt in 10% solution
given:
a%2F%2890+%2B+a%29+=+.1
a+=+.1%2A%2890+%2B+a%29
a+=+9+%2B+.1a
.9a+=+9
a+=+10
Let b = ounces of water in a 15% solution
10%2F%2810+%2B+b%29+=+.15
+10+=+.15%2A%2810+%2B+b%29
10+=+1.5+%2B+.15b
.15b+=+8.5
b+=+56.667
I started with 90 ounces of water, so the decrease must be
90+-+56.667+=+33.333 ounces