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

An assemblage of the most gifted minds in the world were all posed the following question:

"What is 2 + 2 ?"

A mathematician, a physicist, and an engineer were travelling through Scotland when they saw a black sheep through the window of the train. "Aha," says the engineer, "I see that Scottish sheep are black." "Hmm," says the physicist, "You mean that some Scottish sheep are black." "No," says the mathematician, "All we know is that there is at least one sheep in Scotland, and that at least one side of that one sheep is black!"

An engineer, a physicist and a mathematician are staying in a hotel while attending a technical seminar. The engineer wakes up and smells smoke. He goes out into the hallway and sees a fire, so he fills a trashcan from his room with water and douses the fire. He goes back to bed. Later, the physicist wakes up and smells smoke. He opens his door and sees a fire in the hallway. He walks down the hall to a fire hose and after calculating the flame velocity, distance, water pressure, trajectory, etc. extinguishes the fire with the minimum amount of water and energy needed. Later, the mathematician wakes up and smells smoke. He goes to the hall, sees the fire and then the fire hose. He thinks for a moment and then exclaims, "Ah, a solution exists!" and then goes back to bed.