729 ml of a mixture contains milk and water in the ratio of 7 : 2. How much more water is to be added to get a new mixture containing milk and water in the ratio 7 : 3?

A 81 ml

B 710 ml

C 520 ml

D 460 ml

E None of these

Correct Answer: Option A

Since 729 ml of mixture contains milk and water in the ratio 7 : 2,

Amount of milk = (7/9) × 729

= 567 ml

Amount of water = 729 – 567 = 162 ml

Let, x ml of water is added.

⇒ 567 : (162 + x) = 7 : 3

Solving,

x = 81 ml

Hence, we will need to add 81 ml of water to the mixture to make the ratio of milk and water as 7 : 3.