Tính: a) (-3,5).(1 3/5); b) -5/9 . (-2 1/2)

* Hướng dẫn giải

a) $(-3,5).\left(1\frac{3}{5}\right)=\left(\frac{-35}{10}\right)\cdot \left(\frac{1.5+3}{5}\right)=\frac{-7}{2}\cdot \frac{8}{5}=\frac{-7.8}{2.5}=\frac{-7.4}{5}=\frac{-28}{5}$

b) $\frac{-5}{9}\cdot \left(-2\frac{1}{2}\right)==\frac{-5}{9}\cdot \left(-\frac{2.2+1}{2}\right)=\frac{-5}{9}\cdot \left(-\frac{5}{2}\right)=\frac{-5.(-5)}{9.2}=\frac{25}{18}$