A dishonest milkman professes to sell his milk at cost price but he mixes it with water and thereby gains 25%. The percentage of water in the mixture is-

Question: A dishonest milkman professes to sell his milk at cost price but he mixes it with water and thereby gains 25%. The percentage of water in the mixture is-Solution:Let C.P. of 1 litre milk be Tk. 1Then, S.P. of 1 litre of mixture = Tk. 1,Gain = 25%.C.P. of 1 litre mixture = Tk. (100/125) × 1 = Tk. 4/5By the rule of alligation, we have:⇒ Quantity of water : Quantity of milk = (1 - 4/5) : (4/5 - 0) = 1/5 : 4/5 = 1 : 4Hence, percentage of water in the mixture = (1/5) × 100% = 20%