A frog went to visit a fortune teller. "What do you see in my future?" asked the frog.
"Very soon," replied the fortune teller. "you will meet a pretty young girl who will want to know everything about you."
"That's great!" said the frog, hopping up and down excitedly. "But when will I meet her?"
"Next week in science class." said the fortune teller.
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."