Take time to analyze the question. Do not think silently. Let the interviewer KNOW of your thought process.

The answer to this question is:

• First, FILL the 3l VESSEL with WATER.
• Transfer all the water from the 3l vessel into the 5l vessel.
• Refill the 3l vessel again and POUR it off into 5l vessel jug till it is full.
• In the 3l vessel, we now have 1-litre of water available.
• Empty the water from the 5l vessel completely.
• Pour the 1-litre water from 3l vessel to 5l vessel.
• Fill the 3l vessel with water and pour this into the 5l vessel. We now have 4l of water in the 5l vessel.