Tính các tổng sau một cách hợp lí 1/3+-2/6+3/9

* Hướng dẫn giải

a) $\frac{1}{3}+\frac{-1}{3}+\frac{1}{3}=\frac{1}{3}$

$\begin{array}{l}b)\frac{-1}{3}+\frac{2}{5}+\frac{-2}{3}+\frac{4}{5}=\frac{1}{5}\\ \\ c)\frac{7}{23}+\frac{16}{23}+\frac{-5}{9}+\frac{-4}{9}+\frac{-5}{8}=\frac{-5}{8}\\ \\ d)\left(\frac{-2}{9}+\frac{-3}{4}+\frac{-1}{36}\right)+\frac{1}{3}+\left(\frac{3}{5}+\frac{1}{5}\right)=0\\ \\ e)\left(\frac{-1}{2}+\frac{-1}{9}+\frac{-7}{18}\right)+\left(\frac{4}{35}+\frac{3}{5}+\frac{2}{7}\right)=0\end{array}$