A container contains 25 litre of milk. From this container, 5 litre of milk is taken out and replaced by water. This process is further repeated two times. How much milk is there in the container now?

$$\eqalign{ & {\text{Final quantity}} = {\text{Initial quantity}}{\left( {1 - \frac{{{\text{Quantity take out}}}}{{{\text{Capacity of vessel}}}}} \right)^{{\text{Number of process}}}} \cr & = 25{\left( {1 - \frac{5}{{25}}} \right)^3} \cr & = 25{\left( {1 - \frac{1}{5}} \right)^3} \cr & = 25 \times \frac{4}{5} \times \frac{4}{5} \times \frac{4}{5} \cr & = 12.8{\text{ litre}} \cr} $$