You have two jugs with different capacities:

• Jug A can hold exactly 3 liters of water.
• Jug B can hold exactly 5 liters of water.

There is an unlimited supply of water available, but you do not have any measuring tools other than the two jugs. Your task is to measure out exactly 4 liters of water using these two jugs.

Objective:
Find a sequence of steps that allows you to measure exactly 4 liters of water using only the 3-liter and 5-liter jugs.

Solution

This classic puzzle can be solved by carefully pouring water between the two jugs and taking advantage of their different capacities. The key is to use a series of fills, transfers, and empties to reach exactly 4 liters.

Step-by-Step Solution for Water Jug Puzzle:

Step 1: Fill Jug B (5-Liter Jug)

• Fill Jug B to its full capacity with water.
  • Jug A: 0 liters
  • Jug B: 5 liters

Step 2: Pour Water from Jug B into Jug A (3-Liter Jug)

• Pour water from Jug B into Jug A until Jug A is full (3 liters).
  • Jug A: 3 liters
  • Jug B: 2 liters (since Jug B had 5 liters, and 3 liters were poured into Jug A)

Step 3: Empty Jug A

• Empty Jug A completely.
  • Jug A: 0 liters
  • Jug B: 2 liters

Step 4: Transfer Water from Jug B to Jug A

• Pour the remaining 2 liters from Jug B into Jug A.
  • Jug A: 2 liters
  • Jug B: 0 liters

Step 5: Refill Jug B

• Fill Jug B to its full capacity again.
  • Jug A: 2 liters
  • Jug B: 5 liters

Step 6: Pour Water from Jug B into Jug A

• Pour water from Jug B into Jug A until Jug A is full (3 liters). Since Jug A already contains 2 liters, you can only add 1 more liter to it.
  • Jug A: 3 liters
  • Jug B: 4 liters (after transferring 1 liter to Jug A)

Now, Jug B contains exactly 4 liters of water, which is the desired amount.

Final Answer

To measure exactly 4 liters of water:

1. Fill the 5-liter Jug B completely.
2. Pour water from Jug B into Jug A until Jug A is full.
3. Empty Jug A.
4. Transfer the remaining water from Jug B to Jug A.
5. Refill Jug B.
6. Pour water from Jug B into Jug A until Jug A is full.

After these steps, Jug B will contain exactly 4 liters of water.