Three people - an engineer, a chemist and an economist - are stranded on a desert island. Help is on the way, but they have to make due with one can of beans they recovered from the wreckage.
The engineer goes off to try and find some twigs or a rock to try and pry the can open.
The chemist replies, "I have a better idea - lets just soak a corner of the can in the salt water to erode a hole in it."
The economist replies, "I have a better idea... holding everything constant, we have a can opener..."