a)$\frac{1}{5}$ + $\frac{5}{7}$
=$\frac{7}{35}$ + $\frac{25}{35}$
=$\frac{32}{35}$
b) $\frac{1}{5}$×( $\frac{3}{4}$ - $\frac{4}{3}$ )
=$\frac{1}{5}$×($\frac{9}{12}$ -$\frac{16}{12}$ )
=$\frac{1}{5}$×$\frac{-5}{12}$
=$\frac{-1}{12}$
c)$\frac{3}{7}$ -(3$\frac{1}{2}$ + $\frac{2}{7}$ )
=$\frac{3}{7}$ -($\frac{7}{2}$ +$\frac{4}{14}$ )
=$\frac{3}{7}$ -($\frac{49}{14}$ +$\frac{4}{14}$ )
=$\frac{6}{14}$ - $\frac{53}{14}$
=$\frac{47}{14}$
