In a 729 litres mixture of milk and water, the ratio of milk to water is 7 : 2. to get a new mixture containing milk and water in the ratio 7 : 3, the amount of water to be added is:

Answer: Option A

Quantity of milk in 729 litre of mixture
= 7 × $$\frac{729}{9}$$ = 567 litre
Quantity of water
= 729 - 567
= 162 litres
Let x litre of water be added to become ratio 7 : 3

Or, $$\frac{7}{3}$$ = $$\frac{567}{162+\text{x}}$$
Or, 162 × 7 + 7x = 567 × 3
Or, 7x = 1701 - 1134 = 567
Or, x = $$\frac{567}{7}$$ = 81 litres water is to be added.