From the 50 liters of milk, 5 liters of milk is taken out and after it 5 liters of water is added to the rest amount of milk. Again 5 liters of milk and water is drawn out and it was replaced by 5 liters of water. If this process is continued similarly for the third time, the amount of milk left after the third replacement:

Step 1: Understand the process

• Initial quantity of milk = 50 liters
• Each time, 5 liters of the mixture is removed and replaced with 5 liters of water
• This process is done 3 times

Step 2: Use the formula for successive replacement

Formula for quantity of milk left after n operations:

Milk left = Initial quantity × (1 - amount removed / total quantity)ⁿ

Here,

• Initial quantity = 50 liters
• Amount removed = 5 liters
• Total quantity = 50 liters
• n = 3 times

Milk left = 50 × (1 - 5/50)³
          = 50 × (1 - 0.1)³
          = 50 × (0.9)³
          = 50 × 0.729
          = 36.45 liters

Answer: 36.45 liters

After three successive operations of removing 5 liters and replacing with water, 36.45 liters of milk remains in the container.

This type of question involves the concept of successive dilution. It’s a commonly tested topic in aptitude exams, helping learners understand geometric progression and percentage operations in real-life scenarios such as mixing or replacement.