Tính: a) 1 1/2 + 1/5 . [(-2 5/6) + 1/3]; b) 1/3 . (2/5 - 1/2) : (1/6 - 1/5)^2

* Hướng dẫn giải

$$\begin{gathered} a) 1\frac{1}{2}+\frac{1}{5}.\left[\left(-2\frac{5}{6}\right)+\frac{1}{3}\right] \\ =\frac{3}{2}+\frac{1}{5}.\left[\frac{-17}{6}+\frac{2}{6}\right] \\ =\frac{3}{2}+\frac{1}{5}.\frac{-15}{6} \\ =\frac{3}{2}+\frac{\left(-1\right)\mathrm{.3.5}}{\mathrm{5.3.2}}=\frac{3}{2}-\frac{1}{2}=1 \end{gathered}$$

$$\begin{gathered} b) \frac{1}{3}.\left(\frac{2}{5}-\frac{1}{2}\right):{\left(\frac{1}{6}-\frac{1}{5}\right)}^2 \\ =\frac{1}{3}.\left(\frac{4}{10}-\frac{5}{10}\right):{\left(\frac{5}{30}-\frac{6}{30}\right)}^2 \\ =\frac{1}{3}.\frac{-1}{10}:{\left(\frac{1}{30}\right)}^2 \\ =\frac{-1}{30}.{\left(\frac{30}{1}\right)}^2=\frac{-1}{30}.\frac{900}{1}=-30 \end{gathered}$$