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.