In the 75 litres of mixture of milk and water, the ratio of milk and water is 4:1. The quantity of water required to make the ratio of milk and water 3:1 is

Given:

• Total mixture = 75 litres
• Initial milk : water = 4 : 1
• We want to make it milk : water = 3 : 1

Step 1: Find quantity of milk and water in the original mixture

Total parts = 4 + 1 = 5

Milk = (4/5) × 75 = 60 litres

Water = (1/5) × 75 = 15 litres

Step 2: Let x litres of water be added

New water = 15 + x

Milk remains the same = 60 litres

Required ratio: Milk : Water = 3 : 1

⇒ 60 / (15 + x) = 3 / 1 ⇒ 60 = 3(15 + x) ⇒ 60 = 45 + 3x ⇒ 15 = 3x ⇒ x = 5

Answer: 5 litres of water should be added.