如图所示:
=7/20+((8+1/4)-(6+3/5))/(2+3/4)=7/20+((160/20+5/20)-(120/20+12/20))/(40/20+15/20)=7/20+(165/20-132/20)/(55/20)=7/20+(33/20)/(55/20)=7/20+33/55=385/1100+660/1100=1045/1100
如图