$\text{1A Tính}$
$\text{a,}$ `(-1)/21` $\text{+}$ `(-1)/14`
$\text{=}$ `(-2)/42` $\text{+}$ `(-3)/42`
$\text{=}$ `(-2)+(-3)/42`
$\text{=}$ `(-5)/42`
-------------------------------------
$\text{b,}$ `(-1)/9` $\text{-}$ `5/12`
$\text{=}$ `(-4)/36` $\text{-}$ `15/36`
$\text{=}$ `(-4)-(15)/36`
$\text{=}$ `-19/36`
-------------------------------------
$\text{c,}$ `(-14)/20` $\text{+}$ `0,6`
$\text{=}$ `(-7)/10` $\text{+}$ `3/5`
$\text{=}$ `(-7)/10` $\text{+}$ `6/10`
$\text{=}$ `(-7)+6/10`
$\text{=}$ `-1/10`
-------------------------------------
$\text{d,}$ `4,5` $\text{-}$ `(-7/5)`
$\text{=}$ `9/2` $\text{+}$ `7/5`
$\text{=}$ `45/10` $\text{+}$ `14/10`
$\text{=}$ `45+14/10`
$\text{=}$ `59/10`
________________________________________
$\text{1B Tính}$
$\text{a,}$ `(-1)/16` $\text{+}$ `(-1)/24`
$\text{=}$ `(-3)/48` $\text{+}$ `(-2)/48`
$\text{=}$ `(-3)+(-2)/48`
$\text{=}$ `(-5)/48`
-------------------------------------
$\text{b,}$ `(-1)/8` $\text{-}$ `3/20`
$\text{=}$ `(-5)/40` $\text{-}$ `6/40`
$\text{=}$ `(-5)-6/40`
$\text{=}$ `(-11)/40`
-------------------------------------
$\text{c,}$ `(-18)/10` $\text{+}$ `0,4`
$\text{=}$ `(-9)/5` $\text{+}$ `2/5`
$\text{=}$ `(-9)+2/5`
$\text{=}$ `-7/5`
-------------------------------------
$\text{d,}$ `6,5` $\text{-}$ `(-1/5)`
$\text{=}$ `13/2` $\text{+}$ `1/5`
$\text{=}$ `65/10` $\text{+}$ `2/10`
$\text{=}$ `65+2/10`
$\text{=}$ `67/10`
