The ratio(by volume) of milk and water in a mixture is 2 : 1. If we add 12 litres of water in the mixture, then the ratio of milk and water becomes 4 : 3. What is the quantity of water in the new mixture?

36 litres

Initial Mixture,

 Milk : water

  2    :   1 

Final Solution after 12 liters of water is added,

Milk : water

  4    :   3

⇒ Making ratio of Milk in both solutions same, we multiply initial solution with 2,

⇒ (2 : 1) x 2 = 4 : 2,

⇒ Final solution water ratio - Initial solution water ratio = 12 L

⇒ (3 - 2) unit = 12 L

⇒ 1 unit = 12 L,

⇒ The quantity of water in the new mixture = 3 x 12 = 36 liters.