A vessel contains 56 litres of a mixture of milk and water in the ratio 5 : 2. The amount (in litre) of water added to this mixture so that the milk to water ratio becomes 4 : 5 is:

34

The correct answer is Option (3) → 34

$\text{Milk : Water} = 5:2,\ \text{Total} = 56$

$\text{Milk} = \frac{5}{7}\cdot 56 = 40,\quad \text{Water} = 16$

$\text{Let water added} = x$

$\frac{40}{16 + x} = \frac{4}{5}$

$200 = 64 + 4x$

$4x = 136 \Rightarrow x = 34$

$\text{Water added} = 34\ \text{litres}$