Smart Cao Chong knew that the elephant's weight could not be directly weighed, so he converted the elephant's weight into the stone's weight: he first drove the elephant to the boat to get the draft of the boat; Then drive the elephant off the boat and put a few stones on the boat to reach the same draft, so that the weight of the elephant can be obtained by weighing the stones. Cao Chong's thinking method is a transformed thinking method, and the weight of an elephant is measured by the mathematical thinking method of equivalent replacement.