SOLUTION: How much pure water has to be added to a 5% salt solution to end up with 20 gallons of a 3% solution?

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Question 726836: How much pure water has to be added to a 5% salt solution to end up with 20 gallons of a 3% solution?
Answer by josgarithmetic(39617) About Me  (Show Source):
You can put this solution on YOUR website!
VARIABLES TO USE
x = volume of water to use
y = volume of the salt solution to use
M = volume of resulting solution, 20 gallons
H = percent salt solution to use, 5%
T = percent salt solution result for mixture, 3%

MAKE EQUATIONS BASED ON PROBLEM DESCRIPTION
Account for salt. Note very critically, the amount of water and salt solution are both unknown. highlight%28Hy%2F%28x%2By%29=T%29.
...AND, account for materials to use. highlight%28x%2By=M%29.

SOLVE THE SYSTEM
The only unknowns are x and y. Solve this system for x and y.
----------------------------------
highlight%28Hy%2F%28x%2By%29=T%29
highlight%28x%2By=M%29
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COMPUTE VALUES OF x AND y
Substitute the known, given values into the formulas for x and y to find their values.