A dishonest person wants to make a profit on the selling of milk. He would like to mix water (costing nothing) with milk costing 33 $ per litre so as to make a profit of 40% on cost when he sells the resulting milk and water mixture for 36$. In what ratio should he mix the water and milk? Choose the correct choice
A) 1 : 20  B) 1 : 10  C) 17 : 8  D) 17 : 4  E) 17 : 60

Rationale: first of all , let ' s consider 1 liter of the stuff he is going to sell - - - naive customers think it ' s pure milk , but we know it ' s some milk - water mixture . he is going to sell this liter of milk - water for $ 36 . this $ 36 should be a 40 % increase over cost . here , we need to think about percentage increases as multipliers . using multipliers ( cost ) * 1.40 = $ 36 cost = 36 / 1.4 = 360 / 12 = $ 25.71 if he wants a 40 % increase over cost on the sale of one liter of his milk - water , the cost has to be $ 25.71 . well , a liter of milk costs $ 33 , so if he is going to use just $ 30 of milk in his mixture , that ' s 25.71 / 33 = 60 / 77 of a liter . if milk is 60 / 77 of the liter , then water is 17 / 77 of the liter , and the ratio of water to milk is 17 : 60 . answer choice ( e )
Answer: E