$5\frac{2}{10}+7\frac{1}{10}= \frac{52}{10} + \frac{71}{10}=\frac{123}{10}$
$5\frac{6}{7} - 3\frac{5}{7}=\frac{41}{7}-\frac{26}{7}=\frac{15}{7}$
$8\frac{3}{5} \times 2\frac{6}{7}=\frac{43}{5}\times \frac{20}{7}=\frac{860}{35}$
$1\frac{3}{10} : 5\frac{7}{8}=\frac{13}{10}:\frac{47}{8}=\frac{13}{10}\times \frac{8}{47}=\frac{104}{470}$