Shamelessly lifted from reddit:
A physicist, a mathematician and an engineer stay in a hotel.
The engineer is awakened by a smell and gets up to check it. He finds a fire in the hallway, sees a nearby fire extinguisher and after extinguishing it, goes back to bed.
Later that night, the physicist gets up, again because of the smell of fire. He quickly gets up and sees the fire in the hallway. After calculating air pressure, flame temperature and humidity as well as distance to the fire and projected trajectory, he extinguishes the fire with the least amount of fluid.
At last, the mathematician awakes, only again to find a fire in the hallway. He instantly sees the extinguisher and thinks, “A solution exists!”, and heads back into his room.
A variation on a theme:
A group of mathematicians are at a team building seminar. When during the night a fire breaks out in one of the mathematicians room’s. He quickly tears pages out of his notebook lighting them on fire one by one. He then runs down the hall sliding sheets of burning paper under other mathematician’s doors.
After the building burns to the ground the fire marshal asks the mathematicians how the fire spread so fast.
He responds. “I thought distributing the problem would lead to finding a solution faster.”