Đáp án: $\dfrac47$
Giải thích các bước giải:
$(\dfrac{20}7\cdot\dfrac{-4}{-5})+(\dfrac{20}{7}\cdot \dfrac3{-5})$
$=(\dfrac{20}7\cdot\dfrac{4}{5})+(-\dfrac{20}{7}\cdot \dfrac3{5})$
$=\dfrac{20}7\cdot\dfrac{4}{5}-\dfrac{20}{7}\cdot \dfrac3{5}$
$=\dfrac{20}7\cdot (\dfrac45-\dfrac35)$
$=\dfrac{20}7\cdot\dfrac{4-3}{5}$
$=\dfrac{20}7\cdot\dfrac15$
$=\dfrac47$