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. (I really need help setting it up.)

Question

anonymous · Answer

So you begin with 20 ounces and 7% of that is Iodine, that's 1.4 oz.  And it needs to be diluted so that the 1.4oz is 4%, so 1.4/.04 = 35oz

20-->35 oz, so 15oz

anonymous · Answer

I wasn't sure if you meant 7% of the 20 oz was Iodine, or 20oz was 7% of the whole thing.