$\frac{3}{5}$ + $\frac{3}{4}$ : $\frac{4}{7}$ = $\frac{3}{5}$ + $\frac{21}{16}$
= $\frac{153}{80}$
$\frac{1}{2}$ + $\frac{1}{3}$ + $\frac{1}{15}$= $\frac{5}{6}$ + $\frac{1}{15}$
= $\frac{9}{10}$
$\frac{1}{2}$ - $\frac{1}{4}$+ $\frac{1}{6}$= $\frac{1}{4}$ + $\frac{1}{6}$
= $\frac{5}{12}$
$\frac{7}{3}$ + $\frac{4}{3}$ - $\frac{2}{7}$= $\frac{11}{3}$ - $\frac{2}{7}$
= $\frac{71}{21}$
$\frac{2}{5}$ + $\frac{1}{15}$ + $\frac{3}{10}$= $\frac{7}{15}$ + $\frac{3}{10}$
= $\frac{23}{30}$
$\frac{25}{27}$ + $\frac{3}{7}$ + $\frac{4}{7}$ + $\frac{2}{27}$=( $\frac{25}{27}$ + $\frac{2}{27}$ ) + ( $\frac{3}{7}$ + $\frac{4}{7}$ )
= 1 + 1
= 2
6 $\frac{1}{5}$ × 1 $\frac{2}{3}$ : 2= $\frac{31}{5}$ × $\frac{5}{3}$ : 2
= $\frac{31}{3}$ : 2
= $\frac{31}{6}$
