A Physicist, an Engineer, and a Mathematician
A Physicist, an Engineer, and a Mathematician are all locked in separate burning buildings.
The Physicist runs to a chalkboard, calculates exactly how much water he will need to put out the fire, runs and finds that amount, puts out the fire, and survives.
The Engineer pulls out a calculater, calculates exactly how much water he will need to put out the fire, runs and finds 10 times that amount, puts out the fire, and survives.
The mathematician runs to a chalkbaord, calculates exactly how much water he will need to put out the fire, declares, "There is a solution!", and then burns to death. | 
