Correct Answer - Option 5 : 10 litre

**Given **

40 liter milk price at Rs = 25 per kg

**Calculation**

Let the quantity of water to be added be x litres.

Cost of 40 litres of milk at Rs. 25 a litre = 40 × 25 = Rs. 1000

∴ Quantity of the mixture = 40 + x litres

∴ Cost of mixture at Rs. 20 a litre = (40 +x)20 = Rs. (800 + 20x)

∴ 800 + 20x = 1000

or, 20x = 200

∴ x = 10 litres

**Water added in pure milk is = 10 liters**