Đáp án`+`Giải thích các bước giải:

 Bài `11`:

`1) -1/4 + 4/15 - 3/4`

`= (-1/4 - 3/4) + 4/15`

`= -4/4 + 4/15`

`= -15/15 + 4/15`

`= -11/15`

`2) 2/3 - 1/3 + 7/15`

`= 1/3 + 7/15`

`= 5/15 + 7/15`

`= 12/15`

`= 4/5`

`3) 4/5 - (-2/5) - 7/10`

`= 4/5 + 2/5 - 7/10`

`= 6/5 - 7/10`

`= 12/10 - 7/10`

`= 5/10`

`= 1/2`

`4) 3/7 - 2/3 + 4/7`

`= (3/7 + 4/7) - 2/3`

`= 7/7 - 2/3`

`= 1 - 2/3`

`= 3/3 - 2/3`

`= 1/3`

`5) 2/3 + 1/4 - 1/3`

`= (2/3 - 1/3) + 1/4`

`= 1/3 + 1/4`

`= 4/12 + 3/12`

`= 7/12`

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

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

`= 5/5 - 5/4`

`= 1 - 5/4` 

`= 4/4 - 5/4`

`= -1/4`