how many liters of water must be evaporated from 50 liters of a 4 - percent sugar solution to get a 10 - percent solution ?
"4 % of a 50 liter solution is 2 l which is 10 % of the solution at the end . the solution at the end must be 20 l . we need to evaporate 30 liters . the answer is a ."
subtract(50, multiply(divide(50, const_100), 10))