Q:

A vessel contains 20 litres of acid. 4 is taken out of the vessel and replaced by the same quantity of water. Next 4 litres of the mixture are withdrawn, and again the vessel is filled with the same quantity of water. Then find the ratio of acid left in the vessel with the quantity of acid initially in the vessel is:

• 1
  4 : 5
• 2
  4 : 25
• 3
  16 : 25
• 4
  1 : 5