The ratio of milk and water in a mixture is 4 : 3. If we add 2 litres of water, the ratio of milk and water becomes 8 : 7. What is the quantity of the final mixture?

30 litres

Initial Ratio,

 Milk : Water

  4    :    3

2 liters of water is added,

 Milk : Water

  8   :    7

⇒ Making ratio of Milk equal in both the solutions, we multiply Initial solution with 2.

⇒ (4 : 3) x 2 = 8 : 6

⇒ Difference in Initial water ratio and Final water ratio = (7 - 6) = 1 

⇒ 1 unit = 2 liters

⇒ The quantity of the final mixture = (8 : 7) x 2 = 15 x 2 = 30 liters.