Puzzle 44 Solution

Step 1 : Armin + Bob go to the MRT station with the umbrella.
Duration: 4 min

Step 2: Bob returns to school with the umbrella.
Duration: 4 min

Step 3: Chork + Don go to the MRT station with the umbrella.
Duration: 10 min

Step 4: Armin returns to school with the umbrella.
Duration: 3 min

Step 5: Armin + Bob go to the MRT station with the umbrella.
Duration: 4 min

Total duration: 25 min

Answer: 25 min