An engineer, a physicist and a mathematician are staying overnight in a hotel. During the night a fire breaks out. The engineer wakes up, walks out into the hallway, and sees the fire. The engineer grabs a fire extinguisher and puts the fire out.
Later that night the fire breaks out again, but this time the physicist wakes up. The physicist walks out into the hallway and sees the fire. After calculating ambient temperature and air pressure, the physicist puts out the fire.
Later that night, the mathematician wakes up to the smell of smoldering embers. The mathematician walks out into the hall, and thinks for a minute. The mathematician then rekindles the fire from the embers, and goes back to bed satisfied that the problem has been reduced to a previously solved one.
A sociology experiment is conducted involving an engineer, a chemist, and a mathematician. In the first round of experimentation, the participant walks into a room to find a trash can on fire.
The engineer walks in and sees the burning trash can. He pours a bunch of water on it and quenches it.
The chemist walks in and sees the burning trash can. After looking up the MSDS sheet for the contents of the trash can, he likewise pours a bunch of water on it.
The mathematician walks in and sees the trash can. He calculates the precise amount of water needed to quench the fire, and pours it on top, quenching it.
The second round of experimentation has the burning trash can now placed on a desk.
The engineer sees the burning trash can on the desk and again pours water on it.
The chemist walks in to see the trash can is likewise on the table and on fire. He again consults the MSDS sheet, just to be safe, and pours water on the fire.
The mathematician walks in and sees the burning trash can on the table. He picks up the trash can, places it on the floor, and announces, "I have reduced this to a previously solved problem.".