Correct Answer - Option 1 : 40 litres

**Given**

Ratio of milk and water = 4 ∶ 1

10 litres of water is added, then ratio is 3 ∶ 1

**Calculation**

Let the quantity of milk and water is 4x and x

According to question

4x/(x + 10) = 3/1

⇒ 4x = 3x + 30

⇒ 4x - 3x = 30

⇒ x = 30

∴ Quantity of water is 40 litres [(i.e. 30 + 10)]