A container contained 90 litres of milk. Then 9 litres of milk was replaced by water. The process was repeated twice. The volume of milk in container is

A 72.0 litres

B 72.9 litres

C 62.9 litres

D 63 litres

E 81 litres

Correct Answer: Option B

When first 9 litres of milk was replaced by water, then milk left in the container = 90 – 9 = 81 litres

∴ Fraction of milk in the mixture = 81/90 = 9/10 = 0.9

∴when next 9 litres of mixture was being replaced, amount of milk removed = 0.9 × 9 = 8.1 litres

∴ Milk left in the container = 81 – 8.1 = 72.9 litres