In a 40 litre mixture of milk and water, the ratio of milk to water is 3 : 1. How much water (in litres) should be added to make this ratio 2 : 3?

35

Initial quantity of mixture = 40 litres

Initial ratio of milk to water = 3 : 1

Ratio of milk to water after adding milk = 2 : 3

Milk in mixture = (3/4) × 40 = 30

Water in mixture = 40 – 30 = 10

Let x litre water be added

New ratio of milk and water = 2 : 3

⇒ 30 : 10  + x = 2 : 3

⇒ 90 = 20 + 2x

⇒ x = 35