This operation is performed two more times (three operations in all). How many litres of milk remain in the container at the end?

Each operation removes 16/80 = 1/5 of whatever mixture is present, so the milk is multiplied by (1 − 1/5) = 4/5 each time, while the total volume stays 80 litres.

Milk after 3 operations = 80 × (4/5)³ = 80 × 64/125 = 40.96 litres.

Tip: Repeated replacement formula: Final = Initial × (1 − x/V)ⁿ, where x is the quantity drawn each time from volume V.