A Mathematician, a Biologist and a Statistician were sitting in a street cafe watching an apparently empty house on the other side of the street.
Suddenly they noticed two people enter the house. After a while they notice three people coming out of the house.
The Statistician said: “The variation is due to permissible sampling error.”
The Biologist concluded: “They have reproduced.”
The Mathematician said: “If another person goes into the house, it will be empty again!”