SOLUTION: A druggist wants to reduce a 20-ounce quantity of a 7% solution of iodine to a 4% solution by adding pure alcohol. How much alcohol must he add to accomplish this?

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Question 475177: A druggist wants to reduce a 20-ounce quantity of a 7% solution of iodine to a 4% solution by adding pure alcohol. How much alcohol must he add to accomplish this?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let a = ounces of alcohol to be added
In words:
( ounces of iodine in final solution) / ( total ounces of solution) = 4%
given:
Ounces of iodine started with = +.07%2A20+=+1.4+
---------------
+1.4+%2F+%2820+%2B+a%29+=+.04+
+1.4+=+.04%2A%2820+%2B+a%29+
+1.4+=+.8+%2B+.04a+
+.04a+=+.6+
+a+=+15+
15 ounces of pure alcohol must be added