Tính hợp lí a) -3/8 . 2/5 + -3/8 . 14/5 b) (-17 + |91|) - (91 - |-17| - 2019)

* Hướng dẫn giải

a) $\frac{-\text{3}}{\text{8}}\text{.}\frac{\text{2}}{\text{5}}+\frac{-\text{3}}{\text{8}}\text{.}\frac{\text{14}}{\text{5}}=\frac{-3.2}{8.5}+\frac{-3.14}{8.5}$$=\frac{-3}{20}+\frac{-21}{20}=\frac{-24}{20}=\frac{-6}{5}.$

b) $\left(-\text{17}+\left|\text{91}\right|\right)-\left(\text{91}-\left|-\text{17}\right|-\text{2019}\right)$$=\left(-\text{17}+91\right)-\left(\text{91}-17-\text{2019}\right)$ $=-17+91-91+17+2019$ $=\left(-17+17\right)+\left(91-91\right)+2019=2019,$