A little joke shamelessly copied from somewhere else on the Internet:
A physicist, an engineer and a mathemaician were sleeping in the same hotel room when a fire broke out in one corner of the room. Only the engineer woke up; he saw the fire and grabbed a bucket, filled it with water and threw it on the the fire. The fire went out. Then he filled the bucket again and poured that water on the ashes as a safety factor, then he went back to sleep.
A little later another fire broke out in a different corner of the room. Only the physicist woke up. He went over and measured the intensity of the fire, saw what material was burning, then he took the bucket and put enough water to have exactly 2/3 of a bucketful. He poured this on the fire, putting it out perfectly. The physicist went back to sleep.
Later yet another fire broke out in another corner of the room. Only the mathematician woke up. He went over and looked at the fire, he saw that there was a bucket and that it had no holes in it; he turned on the faucet and saw that water was available. Thus, he concluded that a solution to the fire problem existed, so he went back to sleep.