Cao Chong was recognized as an especially gifted and intelligent person from an early age. When he was about six years old his intelligence was thought to be equal to that of an adult.
One day, Sun Quan, who later ruled Eastern Wu in the Three Kingdoms, sent Cao Cao, the de facto ruler of the north, an elephant as a gift. When the elephant was shipped to the capital city of Xuchang, Cao Cao led military and civilian officials, as well as his young son Cao Chong, to see the animal.
Cao Cao had never seen an elephant before. The elephant was big and tall, its legs were as thick as the pillars of a hall, and people could walk under its belly.
Cao Cao said, “This is truly an immense elephant. But how much does it weigh? Does anyone know how we can weigh it?”
This was a good question that started a heated discussion among the officials.
One said, “We have to build a huge scale.”
Another said, “How huge would the scale have to be? And can you ensure that the elephant won’t walk off the scale? The only way I can think of is to kill the elephant and cut it into pieces.”
The others laughed at the official, and argued that his suggestion was a stupid idea. They did not agree to killing the elephant either.
Just then, a boy stepped forward and said, “Daddy, I know how to weigh the elephant.”
Cao Cao was amused and laughed when he saw that it was his son Cao Chong. He said, “You haven’t even come of age yet. What idea have you come up with? Tell me what it is and I will see if it makes sense.”
Cao Chong explained what he was thinking. Cao Cao was very pleased. He immediately gave orders to his guards to prepare to weigh the elephant. Then he told the officials, “Let’s go! We will watch the weighing of the elephant by the river.”
All of the officials followed Cao Cao to the river, where a large boat was docked. Cao Chong asked the guards to guide the elephant onto the boat. When the boat had stabilized, he marked the water level on the body of the boat. He then asked for the elephant to be taken off the boat. He had the guards carry rocks of various sizes onto the boat, which caused the boat to sit lower in the water. By the time the water level reached the line painted on the boat, he asked the guards to stop loading the rocks.
Initially, the officials did not understand what was going on. They quickly understood the process when they saw the water level reach the painted line. They exclaimed, “Good idea! What a good idea!” Everybody had figured out that all one had to do was weigh the rocks and add up the sum to determine the weight of the elephant.