答：1+3分之1-12分之7+20分之9-30分之11+42分之13-56分之15 =1+1/3-(1/3+1/4)+(1/4+1/5)-(1/5+1/6)+(1/6+1/7)-(1/7+1/8) =1+1/3-1/3-1/4+1/4+1/5-1/5-1/6+1/6+1/7-1/7-1/8 =1-1/8 =7/8
答案应该是7/8
答案是8分之7
应该是 7/8
