a)($\frac{1}{4}$+$\frac{-5}{13}$)+($\frac{991}{997}$+$\frac{-8}{13}$+$\frac{3}{4}$) b)$\frac{-1}{7}$.(9$\frac{1}{2}$-8,75):$\frac{2}{7}$+0,625:1$\frac

a) (`1/4`  + `-5/13`) + ( `991/997`+ `-8/13`+ `3/4`)

= `1/4` + `-5/13` +  `991/997`+ `-8/13`+ `3/4`

= ( `1/4` + `3/4`) + ( `-5/13+ `-8/13`) + `991/997`

= `4/4` + `-13/13` + `991/997`

= 1 + (-1) + `991/997`

= 0 + `991/997`

= `991/997`

b)

b) `-1/7` . ( 9  `1/2` – 8,75) : `2/7` +0,625 : 1  `2/3`

  =` -1/7` . (`19/2 `- `35/4` ) .` 7/2` + `5/8` . `3/5`

  = `-1/7` . `3/4` . `7/2` + `3/8`

  = `-3/28 `. `7/2` + `3/8`

  = `-3/8` + `3/8` = 0