One day somebody sent Cao Cao an elephant.Cao Cao wanted to know its weight,but there was nothing big enough to weigh it on.Cao Chong told his father he could weigh the elephant if he had a big boat and a lot of heavy stones.Cao Cao and some other people were very surprised,but still he ordered his men to get everything ready.When they led the elephant down into the boat,the water came up,then Cao Chong marked the water line.Then they drove the elephant onto the bank and put the heavy stones in the boat until the water came up to the same line.At last,Cao Chong told the men to weigh each of the stones.In this way,he weighed the elephant.