During the Period of Three Kingdoms in ancient China, one day, a person gives an elephant to Cao Cao as a present. Cao Cao wants to know the weight of this elephant, but no one has any idea. Then, Cao Caos seven-year-old son Cao Chong says that he has an idea. He asks some servants to carry this elephant to the boat, and marks by the water level of the boat. After that, he asks the servants to carry the elephant out, and put some stones on the boat. When the water level of the boat reaches the former one, Cao Chong asks the servants to carry all the stones out and weigh them. He explains that the weight of the stones is just the weight of the elephant. The people around all praise his cleverness.
