用一根绳去测井深,把绳子3折来量,井口外余3分之4米,把绳子4折来量,井口外余3分之1米,井深多少米?
(4/3-1/3)÷(1/3-1/4)×1/3-4/3
=1÷1/12×1/3-4/3
=4-4/3
=8/3米