Tính nhanh: -3/7 +5/13 +3/7

* Hướng dẫn giải

$a)\frac{-3}{7}+\frac{5}{13}+\frac{3}{7}=\left(\frac{-3}{7}+\frac{3}{7}\right)+\frac{5}{13}=\frac{5}{13}.$

$\begin{array}{l}b)\frac{-5}{21}+\frac{-2}{21}+\frac{8}{24}=\left(\frac{-5}{21}+\frac{-2}{21}\right)+\frac{8}{24}=\frac{-1}{3}+\frac{1}{3}=0\\ \\ c)\frac{-5}{11}+\left(\frac{-6}{11}+2\right)=\left(\frac{-5}{11}+\frac{-6}{11}\right)+2=-1+2=1\\ \\ d)\frac{-1}{32}+\frac{1}{2}+\frac{-15}{32}=\frac{-1}{32}+\frac{-15}{32}+\frac{1}{2}=\frac{-1}{2}+\frac{1}{2}=0\end{array}$