Đáp án + Giải thích các bước giải:

Bài `3:`

`1)` `2/7+6/21-3/14`

`=` `(2.6)/(7.6)+(6.2)/(21.2)-(3.3)/(14.3)`

`=` `12/42+12/42-9/42`

`=` `15/42`

`=` `5/14`

`2)` `(-7)/2+3/4-17/12`

`=` `(-7.6)/(2.6)+(3.3)/(4.3)-17/12`

`=` `(-42)/12+9/12-17/12`

`=` `-50/12`

`=` `-25/6`

`3)` `1/12+1/4+2/3`

`=` `1/12+(1.3)/(4.3)+(2.4)/(3.4)`

`=` `1/12+3/12+8/12`

`=` `12/12`

`=` `1`

`4)` `1/3+(-4)/5-8/15`

`=` `(1.5)/(3.5)+(-4.3)/(5.3)-8/15`

`=` `5/15+(-12)/15-8/15`

`=` `-15/15`

`=` `-1`

`5)` `2/3+(-3)/4+2/6`

`=` `(2.4)/(3.4)+(-3.3)/(4.3)+(2.2)/(6.2)`

`=` `8/12+(-9)/12+4/12`

`=` `3/12`

`=` `1/4`

`6)` `(-5)/18+5/45-9/6`

`=` `(-5)/18+1/9-(9.3)/(6.3)`

`=` `(-5)/18+(1.2)/(9.2)-27/18`

`=` `(-32)/18+2/18`

`=` `-30/18`

`=` `-15/9`

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