a: =12/20+35/20-8/7
=47/20-8/7=169/140
b: =3/7+7/8=24/56+49/56=73/56
c: =9-9/10=9-0,9=8,1
d: =85/30-48/30+9/30=46/30=23/15
\(1)\) \(\dfrac{3}{5}+\dfrac{7}{4}-\dfrac{8}{7}=\dfrac{84}{140}+\dfrac{245}{140}-\dfrac{160}{140}=\dfrac{84+245-160}{140}=\dfrac{169}{140}\)
\(2)\) \(\dfrac{12}{7}:4+\dfrac{7}{8}=\dfrac{12}{7}\times\dfrac{1}{4}+\dfrac{7}{8}=\dfrac{3}{7}+\dfrac{7}{8}=\dfrac{24}{56}+\dfrac{49}{56}=\dfrac{73}{56}\)
\(3)\) \(\dfrac{24}{5}\times\dfrac{15}{8}-\dfrac{9}{10}=9-\dfrac{9}{10}=\dfrac{90}{10}-\dfrac{9}{10}=\dfrac{81}{10}\)
\(4)\)\(\dfrac{17}{6}-\dfrac{8}{5}+\dfrac{3}{10}=\dfrac{85}{30}-\dfrac{48}{30}+\dfrac{9}{30}=\dfrac{85-48+9}{30}=\dfrac{46}{30}=\dfrac{23}{15}\)
\(5)\)\(\dfrac{6}{7}+\dfrac{12}{5}:\dfrac{8}{7}=\dfrac{6}{7}+\dfrac{12}{5}\times\dfrac{7}{8}=\dfrac{6}{7}+\dfrac{21}{10}=\dfrac{60}{70}+\dfrac{147}{70}=\dfrac{207}{70}\)
\(6)\) \(\dfrac{24}{7}-\dfrac{5}{8}\times2=\dfrac{24}{7}-\dfrac{5}{4}=\dfrac{96}{28}-\dfrac{35}{28}=\dfrac{61}{28}\)
