Question 747323
A 60 oz solution has a salt concentration of 20% .  How many ounces of pure salt must be added to the solution to raise its concentration to 25% ? 
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Algebra method:
60*20 + x*100 = (60+x)*25
100x + 1200 = 25x + 1500
75x = 300
x = 4 oz
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A logical method:
60*0.20 = 12 oz of salt --> 48 oz of water.
25% salt --> 75% water
To make 48 oz of water = 75% the total solution = 64 oz
64 - 60 = 4 oz