An engineer Elon, a physicist Stephan and a mathematician Albert are staying overnight in a motel. During the night a fire breaks out. Elon 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 Stephan 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, Albert wakes up to the smell of smoldering embers. The mathematician walks out into the corridor, and thinks for a while. 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.