As the volume of coolant was 02 litres and
Total volume of liquid in car cooling system is 04 liters
Volume of drained water from the car radiator is 2.5 litres
Which means 1.5 litre distilled water was still stuck in car cooling system.
So I required to add 02 litres of coolant and 0.5 litres of distilled in order to achieve 50/50 ratio
of coolant in car cooling system (finally to get 04 liters of diluted coolant).