The clever Cao Chong used the method of "equal replacement". Replace the elephant with many stones, mark the boat, make the elephant and the stone have the same effect, weigh the stones repeatedly, turn "big" into "small", divide and conquer, and this problem will be solved satisfactorily.

Equivalent substitution method is a common scientific thinking method. Here is a short story about Edison. The great American inventor Edison had an assistant named Aptom, who had a good foundation in mathematics. Once, Edison gave Aptom the glass shell of a light bulb and asked him to calculate the volume of the light bulb. Aptom looked at the pear-shaped bulb shell, thought for a long time, drew the sectional view and perspective view of the bulb shell, drew a series of complicated curves, measured the data one by one, and listed a series of formulas. After several hours of intense calculation, the result hasn't come out yet. Edison was very dissatisfied after reading it. I saw Edison fill the bulb shell with water and then pour the water into the measuring cup. In less than a minute, he calculated the volume of the light bulb. Here, Edison replaced the volume of the bulb shell with the volume of water poured into the measuring cup, and also used the equivalent replacement method.

Cao Chongru said in the original text:

When Cao Chong was five or six years old, his knowledge and judgment were comparable to those of an adult. Sun Quan sent a huge elephant. Cao Cao wanted to know the weight of the elephant and asked his subordinates, but all the ministers couldn't figure out how to weigh it. Cao Chong said: "Put the elephant on the big ship, make a mark where the water has not passed the ship, weigh the real thing on the ship and compare it to know the result." Cao Cao was very happy to hear this and immediately acted according to this method.

Cao Chong, who is only six years old, solved a big problem that even many learned adults were at a loss by using the physical principle that the gravity of an object floating on the water is equal to the buoyancy of water on the object. This is a miracle. However, at that time (AD 200), although Archimedes principle had been discovered for 500 years, it was not until 1627 that this principle was introduced to China. It is impossible for George W. Cao Chong to know this truth, let alone the conditions of ups and downs.