joke: Mathematician , Engineer and Chemist

A mathematician, an engineer and a chemist are at a conference. They are staying in adjoining rooms. One evening they are downstairs in the bar. The mathematician goes to bed first. The chemist goes next, followed a minute or two later by the engineer.
The chemist notices that in the corridor outside their rooms a rubbish bin is ablaze. There is a bucket of water nearby. The chemist starts concocting a means of generating carbon dioxide in order to create a makeshift extinguisher but before he can do so the engineer arrives, dumps the water on the fire and puts it out.
The next morning the chemist and engineer tell the mathematician about the fire. She admits she saw it. They ask her why she didn't put it out. She replies contemptuously "there was a fire and a bucket of water: a solution obviously existed