Giải thích các bước giải:
a)$\dfrac{3}{10}$+$\dfrac{4}{7}$:$\dfrac{5}{14}$
=$\dfrac{3}{10}$+ $\dfrac{8}{5}$
=$\dfrac{3}{10}$+ $\dfrac{16}{10}$
=$\dfrac{19}{10}$
b)
$\dfrac{8}{5}$ - $\dfrac{7}{12}$ × $\dfrac{9}{14}$
=$\dfrac{8}{5}$ -$\dfrac{3}{8}$
= $\dfrac{64}{40}$-$\dfrac{15}{40}$
=$\dfrac{49}{40}$