Đáp án+Giải thích các bước giải:
$+)\dfrac{2}{7}+\dfrac{3}{2}=\dfrac{4}{14}+\dfrac{21}{14}=\dfrac{25}{14}\\+)\dfrac{4}{7}.4=\dfrac{16}{7}\\+)\dfrac{7}{8}-\dfrac{2}{5}=\dfrac{35}{40}-\dfrac{16}{40}=\dfrac{19}{40}\\+)\dfrac{9}{5}:\dfrac{8}{15}=\dfrac{9}{5}.\dfrac{15}{8}=\dfrac{27}{8}$