Tính nhanh: 4/7+3/4+2/7+5/4+1/7

* Hướng dẫn giải

$\begin{array}{l}a)\left(\frac{4}{7}+\frac{2}{7}+\frac{1}{7}\right)+\left(\frac{3}{4}+\frac{5}{4}\right)=3\\ \\ b)\left(\frac{-5}{7}+\frac{-2}{7}\right)+\frac{-1}{5}+\left(\frac{3}{4}+\frac{1}{4}\right)=\frac{-1}{5}\end{array}$

$\begin{array}{l}c)\left(\frac{5}{13}+\frac{8}{13}\right)+\frac{-5}{7}+\left(\frac{-20}{41}+\frac{-21}{41}\right)=\frac{-5}{7}\\ \\ d)\left(\frac{1}{28}+\frac{3}{28}\right)+\left(\frac{3}{14}+\frac{-1}{14}\right)+\frac{-1}{7}=\frac{1}{7}\\ \\ e)\left(\frac{1}{2}+\frac{-1}{2}\right)+\left(\frac{-2}{3}+\frac{2}{3}\right)+\left(\frac{3}{4}+\frac{-3}{4}\right)+\left(\frac{-4}{5}+\frac{4}{5}\right)+\left(\frac{5}{6}+\frac{-5}{6}\right)=0\end{array}$