3/5÷(2/3-1/7)×11/12
=3/5÷11/21×11/12
=3/5×21/11×11/12
=21/20
如果你最后是 11/21，则倒数第二步后面两个乘号正好约掉，结果=3/5
3/5÷（2/3-1/7）×11/12=3/5÷11/14x11/12=3/5×14/11×11/12=7/10
