Question

How much water must be evaporated from 64 ounces of a 2% salt solution to make a 10% salt solution?

Answer 1

`64 * 2\%=64 * 0.02=1.28`
64 ounces of a 2% salt solution contains 1.28 ounces of salt and thus 62.72 ounces of water.

The mass of the 10% solution is (x+1.28), where x is the mass of water.
1.28 divided by (x+1.28) must be equal to 10%.

`(1.28)/(x+1.28) * 100\%=10\% \\ (1.28)/(x+1.28) * 100=10 \\ 1.28 * 100=10(x+1.28) \\ 128=10x+12.8 \\ 115.2=10x \\ x=11.52`

The 10% solution contains 11.52 ounces of water.

`62.72-11.52=51.2`

51.2 ounces of water must be evaporated.