How much water needs to be added to a 90 litre mixture of milk and water which is in the ratio of 2 to 1 to change the ratio to 1 to 2?

Answer 1

With a ratio of 2:1 there are 2 + 1 = 3 parts.

Therefore 1 part of 90 litres is 90 litres ÷ 3 = 30 litres.

Thus the mixture currently contains:

• 2 parts milk → 2 × 30 litres = 60 litres of milk; and
• 1 part water → 1 × 30 litres = 30 litres of water.

The final mixture has 1 part milk to 2 parts water.

This time the mixture contains 1 part of milk = 60 litres as calculated above (adding water does not change the volume of milk in the mixture, just the ratio of milk:water).

Thus the amount of water in the final mixture is 2 parts = 2 × 60 litres = 120 litres.

There is already 30 litres of water (as calculated above), so 120 litres - 30 litres = 90 litres of water needs to be added to the original mixture with a ratio of 2:1 to get the final mixture with a ratio of 1:2.

90 litres of water needs to be added.