Correct Answer - Option 4 : 12 L

**Given :**

Quantity of mixture = 20 L

Ratio of milk and water = 2 : 3

**Calculations :**

Quantity of milk = (2/5) × 20 = 8 L

Quantity of water in mixture = 20 - 8 = 12 L

Let x L of water be mixed

⇒ 8/(12 + x) = 1/3

⇒ x = 12

**∴ 12 L of water should be mixed.**