1)
$\frac{65}{38}$ + $\frac{-21}{63}$ = $\frac{157}{114}$
2)
$\frac{2}{3}$ = 0,66;$\frac{9}{10}$=0,9; $\frac{2020}{2021}$=0,999; $\frac{7}{8}$ = 0,875; $\frac{99}{100}$=0,990
Vậy $\frac{2020}{2021}$;$\frac{99}{100}$;$\frac{9}{10}$;$\frac{7}{8}$; $\frac{2}{3}$