b) -3/10 . 7/15 + 3/10 . -8/15 - (-53/10)

* Hướng dẫn giải

$\begin{array}{l}\mathrm{b}) \frac{-3}{10}.\frac{7}{15}+\frac{3}{10}.\frac{-8}{15}-\left(-\frac{53}{10}\right)\\ =\frac{-3}{10}.\frac{7}{15}+\frac{-3}{10}.\frac{8}{15}+\frac{53}{10}\\ =\frac{-3}{10}.\left(\frac{7}{15}+\frac{8}{15}\right)+\frac{53}{10}\\ =\frac{-3}{10}.\frac{15}{15}+\frac{53}{10}\\ =\frac{-3}{10}+\frac{53}{10}\\ =\frac{53-3}{10}\\ =\frac{50}{10}\\ =5\end{array}$