A container contains 40 litres of milk.From this container 4 litres of milk was taken out and replaced by water. This process was repeated further two times. How much milk is now contained by the container.

Amount of milk left after 3 operations

$401-\frac{4}{40}3=40*\frac{9}{10}*\frac{9}{10}*\frac{9}{10}=29.16$ litres