This task is a mathematical challenge ~ and that means that nothing goes wrong ~ engines work ~ people do not need lunchbreaks ~ there are no sneaky shortcuts. Plain logical clear thinking is required.
You are in charge of a squadron of aircraft. You are tasked with flying one of your aircraft all the way around the World. Your aircraft are fitted with special fuel tanks that contain enough fuel to fly exactly half way around the World. All the aircraft have a facility to share fuel with each other ~ whilst in flight ~ instantly. What is the minimum number of aircraft that will be required for all of them to return safely back to base ~ and one of them must travel ~ safely ~ right around the World.
My answer awaits comments to the effect that I am wrong. It is in the subscribers' section [124761] .