解:(X-4)÷X=80%X-4=0.8X0.2X-4=00.2X=4X=20望采纳
(X-4)÷X=80%1-4/X=0.81-0.8=4/x0.2=4/x0.2X=4X=20
(X-4)÷X=80%X-4=80%*X20%*X=4X=4/20%X=20