A mixture contains milk and water in the ratio 4 : 3 (by volume). If 4 litres water is added to it, then the ratio becomes 1: 1. What is the quantity of milk in the initial mixture?

16 litres

Initial Solution,

Milk : Water 

 4    :   3,

After adding 4 liters of water,

Milk : Water 

 1    :   1,

⇒ Making Milk in both solutions equal, we multiply final solution with 4,

⇒ (1 : 1) x 4 = 4 : 4,

⇒ Final solution water ratio - Initial solution water ratio = 4 liters,

⇒ (4 - 3)x = 4 L

⇒ x = 4 L,

Hence, The quantity of milk in the initial mixture = 4 x 4 = 16 liters.