Câu 1: 2 bài đầu hình như đề sai.
\(-\dfrac{5}{6}.\dfrac{4}{17}+-\dfrac{7}{12}.\dfrac{4}{7}\)
\(=\dfrac{4}{7}.\left(-\dfrac{5}{6}+-\dfrac{7}{12}\right)\)
\(=\dfrac{4}{7}.\dfrac{-17}{12}\)
\(=-\dfrac{1}{3}\)
Câu 2:
\(\dfrac{4}{5}.x=125\%-0,25\)
\(\dfrac{4}{5}.x=\dfrac{5}{4}-\dfrac{1}{4}\)
\(\dfrac{4}{5}.x=1\)
\(\Rightarrow\) \(x=1:\dfrac{4}{5}\)
\(\Rightarrow\) \(x=\dfrac{5}{4}\)
Vậy \(x=\dfrac{5}{4}\)
Câu 1:
\(-\dfrac{18}{24}+\dfrac{21}{-56}=-\dfrac{3}{4}+-\dfrac{3}{8}=\dfrac{-6+-3}{8}=-\dfrac{9}{8}\)
\(\left(\dfrac{5}{6}-\dfrac{3}{8}\right):\left(\dfrac{7}{36}-1\right)=\left(\dfrac{20-9}{24}\right):\left(\dfrac{7-36}{36}\right)=\dfrac{11}{24}:\left(-\dfrac{29}{36}\right)=-\dfrac{33}{58}\)
