Mathematician, Biologist, and Physicist
=======================================

   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 Biologist: "They have reproduced".
 The Mathematician: "If now exactly one person enters the house then
 it will be empty again."

Physicist, Engineer, and Mathematician
======================================

   A physicist, an engineer and a mathematician were all in a hotel
 sleeping when a fire broke out in their respective rooms.
   The physicist woke up, saw the fire, ran over to his desk, pulled out
 his CRC, and began working out all sorts of fluid dynamics equations.
 After a couple minutes, he threw down his pencil, got a graduated cylinder
 out of his suitcase, and measured out a precise amount of water.  He threw
 it on the fire, extinguishing it, with not a drop wasted, and went back to
 sleep.
   The engineer woke up, saw the fire, ran into the bathroom, turned on the
 faucets full-blast, flooding out the entire apartment, which put out the
 fire, and went back to sleep.
   The mathematician woke up, saw the fire, ran over to his desk, began
 working through theorems, lemmas, hypotheses , you-name-it, and after a
 few minutes, put down his pencil triumphantly and exclaimed, "I have
 *proven* that I *can* put the fire out!"  He then went back to sleep.

More Physicist, Engineer, and Mathematician
===========================================

When considering the behaviour of a howitzer:
   A mathematician will be able to calculate where the shell will land.
   A physicist will be able to explain how the shell gets there.
   An engineer will stand there and try to catch it.