Cao Chong Weighing the Elephant

Cao Chong’s father, Cao Cao, was a high-ranking official. One day, King Sun Quan presented him with an elephant. He was really curious to know how heavy the elephant was, so he ordered his leading official to think of a way to weigh it. It would certainly be a difficult task. After all, elephants are the largest land animal. How would one go about weighing one?

At the time they didn’t have balances large enough to hold an elephant. Nor did they have the strength to lift up an elephant. Knowing that none of them were able to come up with a method for weighing the elephant, all of the officials became very worried. It was at this time that a small child came running out and while standing in front of the adults said: “I know how! I know how!” As it turned out, when the adults turned to look, it was Cao Cao’s youngest son, Cao Chong, a child around the age of five or six. He told them to lead the elephant down to the riverside with him. His father and all of the officials, very curious to know how he planned to weigh it, followed him to the river.

It just so happened that on the river was a large, empty boat. “Take the elephant onto the boat,” said Cao Chong. As soon as the elephant was aboard, the boat sank a bit deeper into the water.

“Now make a mark on the side of the boat where the water level is,” said Cao Chong. After the mark had been made, Cao Chong called for the elephant to be lead back ashore. Now that the boat was empty it again floated higher on the water. Cao Chong then ordered rocks to be carried onto the boat. As more and more rocks were piled onto the boat, it began to sink back down in the water. “Good! Good!” said Cao Chong as he noticed that the water level had reached the mark made on the side of the boat. Next he ordered the loads of rocks to be taken back onto the shore. It was at this time that everyone finally understood: The rocks that had been loaded onto the boat made the boat sink down to the same level that was marked when the elephant was on the boat. It could now be seen that the elephant and stones were of the same weight. After each rock was weighed and their weight added together, would the sum total reached not equal the weight of the elephant?

“Cao Chong really is brilliant!” said everyone.

Original English translation by Patrick Nowlin, copyright 2013.