A party of people travel in a hot-air balloon. The balloon is blown out to sea, and after many days, land comes into sight again. When floating over the coastline, they see a man walking along a path. One of them shouts: 'Hello! Where exactly are we?' The wanderer looks up, scratches his head, and thinks for some time. Then he shouts: 'You're in the gondola of a hot-air balloon!' That must have been a mathematician. Because: 1) He thought a long time before giving an answer. 2) The answer is absolutely correct. 3) The answer is absolutely useless.