The engineer, physicist, and mathematician were all at a conference hotel, and each woke up to discover a small fire had started in the carpet beside the bed.
The engineer ran to the bathroom, filled the ice bucket with water, and doused the fire, although making a mess in the process.
The physicist used a pocket knife to excise the burning part of the carpet, brought it to the sink, and poured a glass of water on it.
The mathematician went to the bathroom, turned the water on, then off, and got back in bed saying "a solution exists."