2分之3-6分之5+12分之7-20分之9+30分之11-42分之13
=(1+1/2)-(1/2+1/3)+(1/3+1/4)-(1/4+1/5)+(1/5+1/6)-(1/6+1/7)
=1-1/7
=6/7
即7分之6
2分之3-6分之5+12分之7-20分之9+30分之11-42分之13
=(1+1/2)-(1/2+1/3)+(1/3+1/4)-.........(1/6+1/7)
=1+1/2-1/2-1/3+1/3+1/4-1/4-1/5+1/5+1/6-1/6-1/7
=1-1/7
=6/7
7分之6
祝开心
2分之3-6分之5+12分之7-20分之9+30分之11-42分之13
=1+1/2-1/2-1/3+1/3+1/4-1/4-1/5+1/5+1/6-1/6-1/7
=1-1/7
=6/7
2分之3-6分之5+12分之7-20分之9+30分之11-42分之13
=3/2-5/6+7/12-9/20+11/30-13/42
=(1+1/2)-(1/2+1/3)+(1/3+1/4)-..................-(1/6+1/7)
=1+1/2-1/2-1/3+1/3+1/4-1/4-1/5+1/5+1/6-1/6-1/7
=1-1/7
=6/7
3/2-5/6+7/12-9/20+11/30-13/42=6/7
7分之6