A bit of a long joke ...

A sociology experiment involved 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 walked in and saw the burning trash can. He poured a bunch of water on it and quenched it.

The chemist walked in and saw the burning trash can. After looking up the MSDS sheet for the contents of the trash can, she likewise poured a bunch of water on it.

The mathematician walked in and saw the trash can. He calculated the precise amount of water needed to quench the fire, and poured it on top, quenching it.

The second round of experimentation had the burning trash can placed on a desk.

The engineer saw the burning trash can on the desk and poured water again.

The chemist walked in to see the trash can on the table and on fire. She again consulted the MSDS sheet, just to be safe, and poured water on the fire.

The mathematician walked in and saw the burning trash can on the table. He picked up the trash can, placed it on the floor, and announced, "I have reduced this to a previously solved problem."