You are given two buckets of capacities 5 litres and 3 litres respectively. How would you obtain exactly 4 litres of water using only these buckets?
Preambles: 1. The buckets are only two. 2. One of the buckets is 5 litres and the other is 3 litres. 3. They are not marked.
Step 1: Fill the 3litre bucket with water and pour it into the 5-litre bucket.
Step 2: Fill the 3-litre bucket again and gently pour into the 5-litre bucket until it is full to the brim. The water remaining in the 3-litre bucket should now be 1-litre; (3+3)-5 = 1.
Step3. Empty the 5-litre bucket and pour the 1-litre of water from the 3-litre bucket into the 5-litre bucket.
Step4: Finally, fill the 3-litre bucket and pour into the 5-litre bucket already containing 1-litre of water. You now have exactly 4 litres of water in the 5-litre bucket.