为了表达清楚,我增加了括号:(5/18)×9÷(5/18)×27=(5/18)×9×(18/5)×27=9×27=243 (7/9)÷(6/5)+(2/9)÷(6/5)=(7/9)×(5/6)+(2/9)×(5/6)=[(7/9)+(2/9)]×(5/6)=1×(5/6)=5/6 {1-[(1/3)+(1/9)}÷(25/36)={1-(4/9)}×(36/25)=(5/9)×(36/25)=4/5