Let quantity of mixture be x liters. Suppose a container contains x units of liquid from which y units are taken out and replaced by Water. After operations , the quantity of pure liquid = x 1 - y x n units, Where n = no of operations . So, Quantity of Milk = x 1 - 6 x 2 Given that, Milk : Water = 9 : 16 => Milk : (Milk + Water) = 9 : (9+16) => Milk : Mixture = 9 : 25 Therefore, x 1 - 6 x 2 x = 9 25 => x = 15 liters