A vessel having a capacity of 100 liters contains a milk-water solution having 80% milk. The milkman asks his son to add a certain quantity of water to the vessel to reduce the concentration of milk to 60%. The son by mistake added the same quantity of pure milk to the vessel equal to the quantity of water he was asked to add. Realizing his mistake he added twice the quantity of water he was asked to add initially. What was the final concentration of milk in the vessel?