Answer:
52 ounces
Explanation:
You want the number of ounces of pure acid to be added to 300 ounces of 12% acid solution to produce a solution that is 25%.
Setup
Let x represent the number of ounces of acid added. Then the amount of acid in the desired solution is ...
12%(300) +100%(x) = 25%(300 +x)
Solution steps
Subtracting (25%(x) +12%(300)) from both sides, we get ...
75%(x) = 13%(300)
Dividing by the coefficient of x, we find ...
x = (13)(300)/75 = 52
52 ounces of pure acid should be added to make a 25% acid solution.
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Additional comment
In the original solution, there are 12%(300) = 36 ounces of acid. In the 352 ounces of final solution, there will be 36+52 = 88 ounces of acid, a proportion of 88/352 = 1/4 = 25%.