Tính: a) (4/5 - 1): 3/5 - 2/3.0,5 b) 1 - (5/9 - 2/3)^2:4/27 c) [3/8 - 5/12).6 + 1/3].4

* Hướng dẫn giải

$$\begin{gathered} a) \left(\frac{4}{5}-1\right):\frac{3}{5}-\frac{2}{3}.0,5 \\ =\left(\frac{-1}{5}\right):\frac{3}{5}-\frac{2}{3}.\frac{1}{2} \\ =\left(\frac{-1}{5}\right).\frac{5}{3}-\frac{2}{3}.\frac{1}{2} \\ =\left(\frac{-1}{3}\right)-\frac{1}{3} \\ =-\left(\frac{1}{3}+\frac{1}{3}\right)=-\frac{2}{3} \end{gathered}$$

$$\begin{gathered} b) 1-{\left(\frac{5}{9}-\frac{2}{3}\right)}^2:\frac{4}{27}=1-{\left(\frac{5}{9}-\frac{6}{9}\right)}^2:\frac{4}{27} \\ =1-{\left(\frac{-1}{9}\right)}^2.\frac{27}{4}=1-\frac{{(-1)}^2}{9^2}.\frac{27}{4} \\ =1-\frac{1}{81}.\frac{27}{4}=1-\frac{1}{12}=\frac{11}{12} \end{gathered}$$

$$\begin{gathered} c) \left[\left(\frac{3}{8}-\frac{5}{12}\right).6+\frac{1}{3}\right].4=\left[\left(\frac{9}{24}-\frac{10}{24}\right).6+\frac{1}{3}\right].4 \\ =\left(\frac{-1}{24}.6+\frac{1}{3}\right).4=\left(\frac{-1}{=\frac{1}{12}.4=\frac{1}{3}4}+\frac{1}{3}\right).4 \\ =\left(\frac{-3}{}+\frac{4}{12}\right).4 \end{gathered}$$

$$\begin{gathered} d) 0,8:\left\{0,2-7.\left[\frac{1}{6}+\left(\frac{5}{21}-\frac{5}{14}\right)\right]\right\} \\ =\frac{4}{5}:\left\{\frac{1}{5}-7.\left[\frac{1}{6}+\left(\frac{10}{42}-\frac{15}{42}\right)\right]\right\} \\ =\frac{4}{5}:\left\{\frac{1}{5}-7.\left[\frac{1}{6}+\frac{-5}{42}\right]\right\} \\ =\frac{4}{5}:\left\{\frac{1}{5}-7.\left[\frac{7}{42}+\frac{-5}{42}\right]\right\} \\ =\frac{4}{5}:\left\{\frac{1}{5}-7.\frac{1}{21}\right\}=\frac{4}{5}:\left\{\frac{1}{5}-\frac{1}{3}\right\} \\ =\frac{4}{5}:\left\{\frac{3}{15}-\frac{5}{15}\right\}=\frac{4}{5}:\frac{-2}{15}=\frac{4}{5}.\frac{-15}{2}=-6 \end{gathered}$$