A mathematician and an engineer take part in an experiment.

Each is asked to go into a room and do what needs to be done. In the room, there is a waste basket in one corner with some papers in it, and the papers are on fire. In another corner is a small table, and on it is a small pail of water.

The engineer goes in and assesses the situation. He picks up the small pail of water, and pours it over the fire, extinguishing it.

The mathematician goes in the room and assesses the situation. He does the same thing: picks up the pail of water and extinguishes the fire.

The experimenters take note. They then set up part two of the experiment. Again, both the engineer and the mathematician are asked to go into the room and do what needs to be done.

The engineer goes in. Again, there is a waste basket in one corner with some papers in it, and the papers are on fire. The small table is in the same place, but the small pail of water is now on the floor in the middle of the room.

The engineer picks up the water and puts out the fire.

The mathematician's turn. He walks in and sees the same situation: the waste basket with the papers on fire, the table, and the small pail of water in the middle of the room. He picks up the small pail of water and puts it on the table, thereby reducing the second problem to the first problem, which he has already solved.