How much water must be evaporated from 32 ounces of a 4 percent salt solution to make 6 percent salt solution?
Let w = water that must be evaporated
w + 32(0.04) = 0.06(w + 32)
Correct equation set up?
I'm afraid you are very confused. 32 oz of a 4% solution will be 32(0.04) salt but it makes no sense to add w oz of water to 32(0.04) oz of salt!
You can calculate that the solution originally contains 32(0.04)= 1.28 oz of salt. Evaporating x oz of water from0 that means that we have the same amount of salt but 32- x oz of water. The concentration is now 1.28/(32- x)= 0.06. Solve that for x.
My biggest problem now and back in my student days is setting up the right equation leading to the answer. Lacking this skill has kept me away from tutoring jobs in my local area. Tutoring is a great way to make money. As long as I continue to struggle with word problems, tutoring for money is just a distant thought.
You were asked how much water. What are the units?
They are ounces (actually fluid ounces, as opposed to weight).
Your answer would be that there are about 10.67 ounces.
Or, there are exactly $\displaystyle \ 10\tfrac{2}{3} \ $ ounces of water.