There's a man travelling in a hot air balloon. It gets foggy, his GPS runs out of battery, he gets lost. When the fog finally lifts, he sees a great plane with just one single person on it.
He lowers the balloon almost to the ground and when within calling distance, calls to the man:
"My GPS has run out of battery, can you please tell me where I am?"

The man on the ground answers:
"You are in the basket of a hot air balloon, about 10 feet off the ground!"

The man in the balloon:
"You F***ing bastard! Because of you I won't find the way home!"
And after a short pause he adds:
"You must be a mathematician!"

The man on the ground:
"Yes, you are right. How did you know?"

Man in Balloon:
"Your answer was absolutely correct - and absolutely useless!"

Mathematician:
"And you must be a lawyer!"

Man in Balloon:
"Yes - how do you know?"

Mathematician:
"You got lost because you did not bring enough batteries for your GPS. You asked me a question which I correctly answered - and then suddenly you blame me that you are lost!"