Word problem

Question

How much water must be evaporated from 200 L of a 5% salt solution to obtain an 8% salt solution?

Answer 1

In both the 5% and the 8% solutions, the amount of salt with be the same.  In the first situation, salt/200 L = .05, and in the second situation, salt/(200 - evaporated water) = .08.  Solve both equations for the salt:  .05(200) = salt and .08(200-evaporated water) = salt.  Since the amount of salt is the same, .05(200) = .08(200-evaporated water).  Solve the equation:  10 = 16 - .08(evaporated water; -6 = -.08(evaporated water); -6/-.08 = evaporated water; 75 = evaporated water.  75 liters of water must be evaporated from the solution.