Lời giải:
o.
$=\frac{17}{21}+\frac{5}{9}+\frac{-17}{21}+\frac{2}{3}+\frac{4}{9}$
$=(\frac{17}{21}+\frac{-17}{21})+(\frac{5}{9}+\frac{4}{9})+\frac{2}{3}$
$=0+1+\frac{2}{3}=\frac{5}{3}$
p.
$=\frac{13}{5}+\frac{7}{16}+\frac{-15}{16}+\frac{6}{15}$
$=(\frac{13}{5}+\frac{6}{15})+(\frac{7}{16}+\frac{-15}{16})$
$=\frac{45}{15}+\frac{-8}{16}$
$=3-\frac{1}{2}=\frac{5}{2}$
r.
\(=(\frac{-5}{9}+\frac{4}{-9})+(\frac{8}{15}+\frac{7}{15})+\frac{-2}{11}\\ =(\frac{-5}{9}+\frac{-4}{9})+\frac{15}{15}+\frac{-2}{11}\\ =\frac{-9}{9}+\frac{15}{15}+\frac{-2}{11}=-1+1+\frac{-2}{11}=\frac{-2}{11}\)
s.
\(=(\frac{5}{13}+\frac{8}{13})+(\frac{-20}{41}+\frac{-21}{41})+\frac{-5}{17}\\ =\frac{13}{13}+\frac{-41}{41}+\frac{-5}{17}\\ =1+(-1)+\frac{-5}{17}=\frac{-5}{17}\)
