Bài 1: Tính A, -13/15 - 1/-15 B, -3/4 - 2/5 C, 12/-15 - 14/35 Bài 2 : Tính nhanh A, 2/5 + 6/11 + (-2/5) B, 4/15 + 6/15 + (-2/15 + 11/2) Bài 3 : Tính A, 12/-21 --5/35 +2/7 B, 4/18 + -16/48 - 8/12

Bài `1:`

`a)`

        `(-13)/15 - 1/(-15)`

`= -13/15 + 1/15`

`= -12/15= -4/5`

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`b)`

        `-3/4- 2/5`

`= -(3/4+ 2/5)`

`= -(15/20+ 8/20)`

`= -23/20`

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`c)`

        `12/(-15)- 14/35`

`= -( 12/15 + 14/35)`

`= -( 4/5 + 2/5)`

`= -6/5`

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Bài `2:`

`a)`

        `2/5+ 6/11+ (-2/5)`

`= 2/5+ 6/11- 2/5`

`= (2/5- 2/5)+ 6/11`

`= 0+ 6/11= 6/11`

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`b)`

       `4/15+ 6/15 + (-2/15 + 11/2)`

`= 10/15 - 2/15 + 11/2`

`= 8/15 + 11/2`

`= 16/30 + 165/30`

`= 181/30`

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Bài `3:`

`a)`

        `12/(-21)- (-5)/35 + 2/7`

`= -4/7 + 1/7 + 2/7`

`= -(4/7- 1/7- 2/7)`

`= -1/7`

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`b)` 

        `4/18 + (-16)/48 - 8/12`

`= 2/9 - 1/3 - 2/3`

`= 2/9- (1/3 + 2/3)`

`= 2/9- 1`

`= -7/9`

`#` $kiddd$