An engineer, a physicist, and a mathematician are attending a conference. They stay in hotel rooms with walls that meet at a common corner.
An outlet in the corner shorts out and starts a fire. The engineer runs for his room's fire extinguisher, douses the outlet, then douses the wall for a two foot radius around. He then starts writing a log and observes it for the next two hours.
The physicist does a quick calculation on a notepad, gets his fire extinguisher, and douses his wall with one precise burst. He is satisfied after ten minutes that he's put it out.
The mathematician stares at the fire in his wall, thinks for a moment, then runs into the bathroom and runs water on his hand. He nods and goes back to bed.