3a nha
3A:
a: \(\left(-0,25\right)\cdot\dfrac{4}{17}\cdot\left(-3\dfrac{5}{21}\right)\cdot\dfrac{-7}{23}\)
\(=\dfrac{-1}{4}\cdot\dfrac{4}{17}\cdot\dfrac{-68}{21}\cdot\dfrac{-7}{23}\)
\(=-\dfrac{1}{17}\cdot\dfrac{68}{21}\cdot\dfrac{7}{23}\)
\(=-\dfrac{68}{17}\cdot\dfrac{7}{21}\cdot\dfrac{1}{23}=-\dfrac{1}{23}\cdot\dfrac{1}{3}\cdot4=-\dfrac{4}{69}\)
b: \(\dfrac{-2}{5}\cdot\dfrac{4}{15}+\left(-\dfrac{3}{10}\right)\cdot\dfrac{4}{15}\)
\(=\dfrac{4}{15}\cdot\left(-\dfrac{2}{5}-\dfrac{3}{10}\right)\)
\(=\dfrac{4}{15}\cdot\dfrac{-7}{10}=\dfrac{-28}{150}=-\dfrac{14}{75}\)
c: \(21-3\dfrac{3}{4}:\left(\dfrac{3}{8}-\dfrac{1}{6}\right)\)
\(=21-\dfrac{15}{4}:\left(\dfrac{9}{24}-\dfrac{4}{24}\right)\)
\(=21-\dfrac{15}{4}:\dfrac{5}{24}=21-\dfrac{15}{4}\cdot\dfrac{24}{5}\)
\(=21-18=3\)
d: \(\left(-\dfrac{5}{6}+\dfrac{2}{5}\right):\dfrac{3}{8}+\left(\dfrac{4}{5}-\dfrac{11}{30}\right):\dfrac{3}{8}\)
\(=\left(-\dfrac{5}{6}+\dfrac{2}{5}+\dfrac{4}{5}-\dfrac{11}{30}\right):\dfrac{3}{8}\)
\(=\left(-\dfrac{25}{30}+\dfrac{36}{30}-\dfrac{11}{30}\right):\dfrac{3}{8}\)
=0
