a) $\dfrac{7}{30}+\dfrac{-12}{37}+\dfrac{23}{30}+\dfrac{-25}{37}=\left(\dfrac{7}{30}+\dfrac{23}{30}\right)+\left(\dfrac{-12}{37}+\dfrac{-25}{37}\right)=1+\left(-1\right)=0$b) $\dfrac{1}{2}+\dfrac{13}{19}-\dfrac{4}{9}+\dfrac{6}{19}+\dfrac{5}{18}=\left(\dfrac{1}{2}-\dfrac{4}{9}+\dfrac{5}{18}\right)+\left(\dfrac{13}{19}+\dfrac{6}{19}\right)=\dfrac{1}{3}+1=\dfrac{1}{3}+\dfrac{3}{3}=\dfrac{1+3}{3}=\dfrac{4}{3}$c) $\dfrac{-20}{23}+\dfrac{2}{3}-\dfrac{3}{23}+\dfrac{2}{5}+\dfrac{7}{15}=\left(\dfrac{-20}{23}-\dfrac{3}{23}\right)+\left(\dfrac{2}{3}+\dfrac{2}{5}+\dfrac{7}{15}\right)=\left(-1\right)+\dfrac{23}{15}=\dfrac{8}{15}$Câu trả lời: a) $\dfrac{7}{30}+\dfrac{-12}{37}+\dfrac{23}{30}+\dfrac{-25}{37}=\left(\dfrac{7}{30}+\dfrac{23}{30}\right)+\left(\dfrac{-12}{37}+\dfrac{-25}{37}\right)=1+\left(-1\right)=0$b) $\dfrac{1}{2}+\dfrac{13}{19}-\dfrac{4}{9}+\dfrac{6}{19}+\dfrac{5}{18}=\left(\dfrac{1}{2}-\dfrac{4}{9}+\dfrac{5}{18}\right)+\left(\dfrac{13}{19}+\dfrac{6}{19}\right)=\dfrac{1}{3}+1=\dfrac{1}{3}+\dfrac{3}{3}=\dfrac{1+3}{3}=\dfrac{4}{3}$c) $\dfrac{-20}{23}+\dfrac{2}{3}-\dfrac{3}{23}+\dfrac{2}{5}+\dfrac{7}{15}=\left(\dfrac{-20}{23}-\dfrac{3}{23}\right)+\left(\dfrac{2}{3}+\dfrac{2}{5}+\dfrac{7}{15}\right)=\left(-1\right)+\dfrac{23}{15}=\dfrac{8}{15}$