Explanation:

Given that container has 50 litres of milk.

 After replacing 8 litres of milk with water for three times, milk contained in the container is:

 ⇒[50(1−8/50)³]

⇒(50×42/50×42/50×42/50)

 = 29.63 litres.

Hence, option 1 is the correct answer.