1/12+9/20-1/30-13/42+1/56 1/3+3/4+2/5+5/7+7/8+9/20+10/21+11/24+19/35

...1\/3+3\/4+2\/5+5\/7+7\/8+9\/20+10\/21+11\/24+19\/35
1\/12+9\/20-1\/30-13\/42+1\/56 =1\/3-1\/4+1\/4+1\/5-1\/5+1\/6-1\/6-1\/7+1\/7+1\/8 =1\/3+1\/8 =11\/24 1\/3+3\/4+2\/5+5\/7+7\/8+9\/20+10\/21+11\/24+19\/35 =1\/3+3\/4+2\/5+5\/7+7\/8+1\/4+1\/5+1\/3+1\/7+1\/3+1\/8+1\/5+2\/7 =（1\/3+1\/3+1\/3）+（3...

1\/12+9\/20-1\/30-13\/42+1\/56,
1\/12+9\/20-1\/30-13\/42+1\/56 =(1\/3-1\/4)+(1\/4+1\/5)-(1\/5-1\/6)-(1\/6+1\/7)+1\/7-1\/8 =1\/3-1\/4+1\/4+1\/5-1\/5+1\/6-1\/6-1\/7+1\/7-1\/8 =1\/3-1\/8 =5\/24

12分之1+20分之9-30分之1-42分之13+56分之1的简便运算。
1\/12+9\/20-1\/30-13\/42+1\/56 ={（1\/12+9\/20-1\/30-13\/42+1\/56）*840}\/840 =（70+378-28-260+15）\/840 =35\/168 =5\/24

麻烦解决一道计算题(要伴有巧算过程)
1\/12+9\/20-1\/30-13\/42+1\/56 =1\/3-1\/4+1\/7-1\/8-（1\/5-1\/6）+9\/20-13\/42 =（1\/3+1\/6-3\/8）+（-1\/5+9\/20）+（1\/7-13\/42）=1\/8+1\/4-1\/6 =3\/8-1\/6 =5\/24

一又1\/3-7\/12+9\/20-11\/30+13\/42-15\/56简便运算
原式=(1+1\/3)-(1\/3+1\/4)+(1\/4+1\/5)-(1\/5+1\/6)+(1\/6+1\/7)-(1\/7+1\/8)，打开括号，相邻两项相消，原式=1-1\/8=7\/8

1\/3+3\/4+2\/5+5\/7+7\/8+9\/20+10\/21+11\/24+19\/35
1\/3+3\/4+2\/5+5\/7+7\/8+9\/20+10\/21+11\/24+19\/35 =(1\/3+3\/4+7\/8+11\/24)+(2\/5+9\/20)+(5\/7+10\/21+19\/35)=(8\/24+18\/24+21\/24+11\/24)+(8\/20+9\/20)+(75\/105+50\/105+57\/105)=29\/12+17\/20+26\/15 =145\/60+51\/60+104\/60 =300\/60 =5 ...

...1+3\/2-5\/6+7\/12-9\/20+11\/30-13\/42+15\/56-17\/72+19\/90-21\/110=...
1+（1+1\/2）-（1\/2+1\/3）+（1\/3+1\/4）……-（1\/10+1\/11）=1+1-1\/11 =1又10\/11

...1-5\/6+7\/12-9\/20+11\/30-13\/42+15\/56-17\/72+19\/90
第N个数等于N分之一加N+1之一,前年加上正负号就可以抵消了,如1-（1\/2+1\/3）+（1\/3+1\/4）…1-(1\/2+1\/3)+(1\/3+1\/4)-(1\/4+1\/5).-(1\/8+1\/9)+(1\/9+1\/10)=1-1\/2-1\/3+1\/3+1\/4.-1\/8-1\/9+1\/9+1\/10 =1-1\/2+1\/10 =6\/10 =3\/5 ...

1-5\/6+7\/12-9\/20+11\/30-13\/42+15\/56这道题用简便方法杂做?
这种多项分数加减的题目，多数是用所谓的列项法来做。其中5\/6=1\/2+1\/3依次下去。所以原式=1-（1\/2+1\/3）+（1\/3+1\/4）-（1\/4+1\/5）+...=1-1\/2-1\/3+1\/3...-1\/7+1\/7+1\/8 =1\/2+1\/8=5\/8

1\/2+5\/6-7\/12+9\/20-11\/30+13\/42-15\/56 简便计算 快
等于 1\/2+1\/2+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