Đáp án`+`Giải thích các bước giải:

`b)`

`(-5)/12 . 2/11 +(-5)/12 . 9/11 +5/12`

`=(-5)/12 . (2/11 +9/11) +5/12`

`=(-5)/12 . 11/11 +5/12`

`=(-5)/12 .1 +5/12`

`=-5/12 +5/12`

`=0`

`d)` `5/(2.4) +5/(4.6) +5/(6.8) +...+5/(48.50)`

`=5. 1/2 (2/(2.4) +2/(4.6) +2/(6.8) +...+2/(48.50))`

`=5/2 (1/2 -1/4 +1/4 -1/6 +1/6 -1/8 +....+1/48 -1/50)`

`=5/2 (1/2 -1/50)`

`=5/2 . 12/25`

`=60/50`

`=6/5`