1200 ml of mixture contains milk and water in the ratio of 5 : 3. What amount of water should be added to make the ratio 5 : 4?

1200 ml mixture contains milk and water in ratio of 5:3

∴ Amount of milk in mixture $(= \frac{5}{{5 + 3}} \times 1200 = \frac{5}{8} \times 1200 = 750\;ml)$

∴ Amount of water in mixture = 1200 – 750 = 450 ml

Let’s assume that ‘x’ ml of water is added to 1200 ml of mixture so that the ratio of milk to water becomes 5:4. The total amount of milk does not change.

Total amount of water = 450 + x

? the required ratio of milk to water is 5:4,

$(\Rightarrow \frac{{750}}{{450\; + \;x\;}} = \frac{5}{4})$

⇒ 4 × (750) = 5 × (450 + x)

⇒ 3000 = 2250 + 5x

⇒ 750 = 5x

⇒ x = 750/5 = 150 ml.

∴ 150 ml of water has to be added.