20 litres from a vessel completely filled with milk is replaced by water and then again 20 litres of the new mixture is replaced by water. If 18 litres of milk is left now in the vessel, what was the capacity of the vessel?
The correct option is C 50 litres
Using the formula, we get x (1−(20x))2=18⇒x(1−(40x)+(400x2))=18
Solving, we get x = 50 litres