Hướng dẫn trả lời:
$\text{a) $\dfrac{37}{60}$ - $\dfrac{31}{36}$.}$
$\text{= $\dfrac{111}{180}$ - $\dfrac{155}{180}$.}$
$\text{= $\dfrac{111 - 155}{180}$.}$
$\text{= $\dfrac{-44}{180}$.}$
$\text{= $\dfrac{-11}{45}$.}$
$\text{b) $\dfrac{1}{-3}$ + $\dfrac{2}{5}$ - $\dfrac{-4}{7}$.}$
$\text{= $-\dfrac{1}{3}$ + $\dfrac{2}{5}$ + $\dfrac{4}{7}$.}$
$\text{= $(-\dfrac{1}{3}$ + $\dfrac{2}{5})$ + $\dfrac{4}{7}$.}$
$\text{= $(-\dfrac{5}{15}$ + $\dfrac{6}{15})$ + $\dfrac{4}{7}$.}$
$\text{= $\dfrac{1}{15}$ + $\dfrac{4}{7}$.}$
$\text{= $\dfrac{7}{105}$ + $\dfrac{60}{105}$.}$
$\text{= $\dfrac{67}{105}$.}$
$\text{c) $\dfrac{270}{405}$ + $\dfrac{152}{-380}$.}$
$\text{= $\dfrac{270}{405}$ - $\dfrac{152}{380}$.}$
$\text{= $\dfrac{2}{3}$ - $\dfrac{2}{5}$.}$
$\text{= $\dfrac{10}{15}$ - $\dfrac{6}{15}$.}$
$\text{= $\dfrac{4}{15}$.}$
