A 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 of 7:3?

Correct option is A

Let the amount of milk is 7x while the amount of water is 2x in the mixture. Now, we have a total of 729 mL of the mixture. Thus,
7x + 2x = 729
9x = 729
x = 729/9 = 81 Thus, the amount of milk
7x = 7 × 81
7x = 567 mL
Amount of water
2x = 2 × 81
2x = 162 mL
x= 81 mL
Now, the new mixture has a ratio of 7:3.
For this, the amount of milk will be 7x and the amount of water is 3x.
Here, the quantity of milk is the same while the quantity of water is increasing. This increased quantity is,
3x − 2x = x
3x − 2x = 81 mL