A solution of salt and water contains 15% salt. If 30 lt water is evaporated from the solution the concentration becomes 20% salt. Find the original volume of the liquid before water evaporated.
a. 100 lt                        b. 120 lt                       c. 200 lt            d. None


let 'x' be the quantity of solution of salt and water
Salt content before evaporation of water= 15% of x = 0.15x (x = volume of solution)
Salt content after evaporation of water = 20% of [x-30] = 1/5  (since 30 lt evaporated)
equating both of them

(15/100) * x = (20/100) * (x-30)
3x/20 = 1/5 * (x - 30)
3x/20 - 1/5x = - 30/5
15x- 20x = - (6*20*5)
- 5x = -(6*20*5)
x = 120 litres