Two physicists were riding in a hot air balloon and were blown off course sailing over a mountain trail, and were completely lost. They spotted a jogger running on the trail and they shouted, "Can you tell us where we are?"
After a few minutes, the jogger yelled back, "You're up in a balloon."
One physicist says to the other, "Just our luck to run into a mathematician!"
"How do you know he was a mathematician?" asked the other.
"First, he took a long time to answer. Second, his answer was 100% correct. And third, it was totally useless!"