Tính nhanh: a) 9/8 - 4/7 + -1/8 + 11/7 b) -5/7 . 3/11 + -5/7 . 8/11 + 5/7

* Hướng dẫn giải

a) 

$\begin{array}{l}\frac{9}{8}-\frac{4}{7}+\frac{-1}{8}+\frac{11}{7}\\ =\left(\frac{9}{8}+\frac{-1}{8}\right)+\left(-\frac{4}{7}+\frac{11}{7}\right)\\ =1+1\\ =2\end{array}$

b)

$\begin{array}{l}\frac{-5}{7}\cdot \frac{3}{11}+\frac{-5}{7}\cdot \frac{8}{11}+\frac{5}{7}\\ =\frac{-5}{7}\left(\frac{3}{11}+\frac{8}{11}-1\right)\\ =\frac{-5}{7}.0\\ =0\end{array}$