Basic mathematics

A Mathematician, a Biologist and a Physicist are sitting in a street cafe watching people going in and coming out of the house on the other side of the street.

First they see two people going into the house. Time passes. After a while they notice three persons coming out of the house.

The Physicist: "The measurement wasn't accurate.".

The Biologists conclusion: "They have reproduced".

The Mathematician: "If now exactly 1 person enters the house then it will be empty again."

An chemist, a physicist, and a mathematician are stranded on an island when a can of food rolls ashore.

The chemist and the physicist comes up with many ingenious ways to open the can.

Then suddenly the mathematician gets a bright idea: "Assume we have a can opener ..."