On one occasion, his father was presented an elephant by the southern envoy. It was a so very tall and large animal that no one had ever seen at that time in Northern China. A question suddenly came up into the father’s mind: how much of its weight? The understrappers, accordingly, assigned dozens of solders to build a huge balance with a big plate, where the elephant is to be placed and weighted. However, the elephant is so heavy that wooden weighbeam can not sustain its weight and cracked. Some one suggest to kill the elephant, weight each parts of it and thereby put them together, but still no one can work out of any good idea to weight an alive elephant.
Right at this moment, seven-year-old Cao Chong jumped out and said to his father: "I can weight it." The surprised father smiled: "You are only a little boy, what is your mean? You talk about it." Cao Chong winked naughtily: “follow me and just do what I required”, then ran onwards to the lake of the palace. Those adults who saw that all shaked their heads, showing unbelievable expression and considering it was just a little joke. But the father abandoned his dubitation, he called others to follow the little son to the lake to see how the elephant was to be weighted.
By the lake, Cao Chong firstly asked some one to lead the elephant to a boat. After the boat became stabilized, he marked two sighs on both sides at the horizontal of the water surface. Then, he disembarked the elephant; in replace, some rocks were moved onto the boat until the mark placed in the hull reached the horizontal again. People who saw that all applauded and erected their thumbs. At this time everyone knows that, as long as those stones were weighted, the elephant’s weight could be easily derived. Seeing the little son Cao Chong smarter than adults, the father delighted so much.