Đáp án:
Giải thích các bước giải:
a)$\dfrac{5}{4}$ + $\dfrac{6}{7}$ x $\dfrac{2}{9}$ =
$\dfrac{5}{4}$ + $\dfrac{12}{63}$
=$\dfrac{315}{252}$ + $\dfrac{48}{252}$
= $\dfrac{363}{252}$ = $\dfrac{121}{84}$
b) $\dfrac{7}{9}$ - $\dfrac{4}{15}$ :$\dfrac{2}{5}$
=$\dfrac{7}{9}$ - $\dfrac{4}{15}$ x $\dfrac{2}{5}$
= $\dfrac{7}{9}$ - $\dfrac{20}{75}$
= $\dfrac{525}{675}$ - $\dfrac{180}{675}$
=$\dfrac{375}{675}$ = $\dfrac{125}{225}$ = $\dfrac{25}{45}$ = $\dfrac{5}{9}$
