A mixture contains milk and water in the ratio of 5 : 3, respectively. On adding 7 litres of water, the ratio of milk to water becomes 1 : 2. Find the quantity of milk in the mixture.

5 litres

Initial mix ,

M : W = 5 : 3,  ..(1.)

After adding 7 litre water,

M : W = 1 : 2,   ..(2.)

So, making the unit of milk in both ratios same,

we multiply eq. (2.) with 5,

(1 : 2) x 5 = 5 : 10,

Difference between and initial and after quantity of water = 10 - 3 = 7,

Therefore, 7 units = 7 litres,

1 unit = 1 litre,

Hence, quantity of milk is = 1 x 5 = 5 litres.