John has 20 ounces of a 20% of salt solution. How much water should he evaporate to make it a 30% solution?

Question

I need to know what kind of problem it is and what that problem is.

Answer 1

Since it asks the amount of water to be evaporated (subtracted) the solutions must be in terms of water.

20% salt is 80% water

30% salt is 70% water

 

(0.80)(20) - w = (0.70)(20 - w)

 

Can you solve for w and answer?