5/(7/13)/(13/16)/(16/19)/(19/21)
=5*7/13*13/16*16/19*19/21
=5*7/21
=5*1/3
=5/3这样是错的吧没错仔细看一下吧没错郁闷5/(7/13)/(13/16)/(16/19)/(19/21) =5/(7/13*13/16*16/19*19/21) =5/(7/21) =5/(1/3)=5*3=15也错的