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 calculator, 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 chalkboard, calculates exactly how much water he will need to put out the fire, declares, “There IS a solution!”, and then burns to death.