Two men are in a hot air balloon. It is so foggy that the men cannot

Two men are in a hot air balloon. It is so foggy that the men cannot

see each other in the basket, much less see anything beyond the basket. One of the men yells, "Where are we?"

There is a long silence.

From the other side of the basket, a voice yells, "In a balloon!"

How can you tell the other man was a mathematician? 1: It took him a long time to get the answer. 2: The answer was absolutely correct. 3: The answer had no application in real life.