Tính nhanh: a) 5/7 . 10/11 + 5/7 .14/11 - 5/7 .17/11 b) 1/3 . 4/5 + 1/3

* Hướng dẫn giải

a)

$\begin{array}{l}\frac{5}{7}\cdot \frac{10}{11}+\frac{5}{7}\cdot \frac{14}{11}-\frac{5}{7}\cdot \frac{17}{11}\\ =\frac{5}{7}\left(\frac{10}{11}+\frac{14}{11}-\frac{17}{11}\right)\\ =\frac{5}{7}.1\\ =\frac{5}{7}\end{array}$

b)

$\begin{array}{l}\frac{1}{3}\cdot \frac{4}{5}+\frac{1}{3}\cdot 1\frac{1}{5}-{\left(\frac{-2}{3}\right)}^1\\ =\frac{1}{3}\cdot \frac{4}{5}+\frac{1}{3}\cdot \frac{6}{5}+\frac{2}{3}\\ =\frac{1}{3}\left(\frac{4}{5}+\frac{6}{5}\right)+\frac{2}{3}\\ =\frac{1}{3}.2+\frac{2}{3}\\ =\frac{4}{3}\end{array}$