Đáp án + giải thích các bước giải:

`a)` `(-5)/8:(1/2-3/4)+5/7`

`=(-5)/8:(-1)/4+5/7`

`=5/2+5/7`

`=45/14`.

`b)` `1,5-5/9*(0,25-13/10)`

`=3/2-5/9*(1/4-13/10)`

`=3/2-5/9*(-21)/20`

`=3/2-(-7/12)`

`=25/12`.

`c)` `5/1.4+5/4.7+5/7.10+...+5/102.105`

`=5/3(3/1.4+3/4.7+3/7.10+...+3/102.105)`

`=5/3(1-1/4+1/4-1/7+1/7-1/10+...+1/102-1/105)`

`=5/3(1-1/105)`

`=5/3*104/105`

`=104/63`.