A mathematician, a physicist, and an engineer are at a hotel one
night sleeping after the first day of a conference.
A disgruntled hotel employee decides to get even with the
management. He goes to a floor where there is nobody in the hallway.
He drops a lit match into a trashcan in the hallway.
The engineer wakes up and smells smoke. He goes out into the
hallway and sees a fire, so he fills his trash can from his room with
water and douses the fire. He goes back to bed.
The disgruntled hotel employee found another trash can in the
hallway and drops a lit match into it. 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
distance, water pressure, trajectory, etc. extinguishes the fire with
the minimum amount of water and energy needed. He goes back to bed.
This hotel employee then drops some trash paper and a lit match
into the same trash can in the hallway. Then the mathematician wakes
up and smells smoke. He goes to the hallway, sees a fire and then the
fire-hose. He thinks for a moment and then exclaims, "Ah, a solution
exists!!" and then goes back to bed.