Seaplane Puzzle - Solution
The Puzzle:
You need to fly once around the world.
You have 3 seaplanes and lots of fuel, but a full tank lasts only halfway around the world.
You can land and take off anywhere, transferring fuel as needed.
Can you get around the world, ending up with all planes safe at the start?
Our Solution:
Divide the distance into 6 equal legs (3 legs = halfway)
• 2 planes fly to the first leg, fuel up one plane which continues to the second leg and the first plane goes back to the start.
• again 2 planes fly to the first leg, fuel up one plane which continues to the second leg and the first plane goes back to the start.
• We now have 2 planes at the second leg, and each is 2/3 full. One of them fuels up the other one and goes back to the first leg, where it meets the third plane which comes from the start to supply it with 1/3 fuel so they can both can return to the start. In the meantime, the other plane at the second leg having a full tank flies to the 5th leg
• one (of the two) plane from the start can now go to the 5th leg (which is only one leg away the opposite direction), share its remaining fuel and both planes return safely to the start.