There's an engineer, a physicist, and a mathematician and they are all attending a convention at some hotel.

There's an engineer, a physicist, and a mathematician and they
are all attending a convention at some hotel. A fire breaks out
when everyone is asleep. The engineer wakes up, smells the smoke,
gets up, runs out into the hallway, runs to the nearest firehose,
and douses the entire room with water. All of the engineer's
possesions were wet, but at least he was safe.
The physicist wakes up, smells the smoke, whips out pencil
and paper, writes a few equations down, then rushes into the bathroom
to fill a cup of water, and then throws the cup of water in the
exact spot in the room to douse all the flames.
The mathematician wakes up, smells the smoke, thinks for a minute,
then rushes into the bathroom, fills a cup of water, lights a match,
sticks the match in the cup. Seeing that flame was extinguished,
the mathematician proclaims, "Ah! A solution exists." Then he
goes back to sleep.