[CurtMonash]

A poor mathematician had a very dodgy gas stove. Indeed, it caused a small fire. So he quickly filled a pot with water and put the fire out.

A few days later, it happened again. This time, there happened to be a pot filled with water, waiting to be used.

So he emptied the pot, thus reducing the problem to one he already had solved.

[xigoi]

A mathematician was working when she noticed that her trash bin is burning. She turned around and saw a fire extinguisher. “Clearly the problem has a solution”, she said to herself and went back to work.