1+1/2-六分之五+7/12-20分之9+11/30-42分之13=几分之几

原式=1+1/2-(1/2+1/3)+(1/3+1/4)-(1/4+1/5)+(1/5+1/6)-(1/6+1/7)
=1+1/2-1/2-1/伏卜3+1/3+1/4-1/4-1/闷桥5+1/5+1/6-1/6-1/7
=1-1/7
=6/蚂厅猛7