Bài 4:
\(\dfrac{-7}{15}\cdot\dfrac{5}{8}\cdot\dfrac{15}{-7}\cdot\left(-32\right)\)
\(=\left(\dfrac{-7}{15}\cdot\dfrac{15}{-7}\right)\cdot\left(\dfrac{5}{8}\cdot-32\right)\)
\(=1\cdot\dfrac{5\cdot-32}{8}\)
\(=1\cdot5\cdot-4\)
\(=-20\)
⇒ C
Bài 5:
\(2x+\dfrac{1}{2}=5\dfrac{1}{2}\)
\(\Rightarrow2x+\dfrac{1}{2}=5+\dfrac{1}{2}\)
\(\Rightarrow2x=5\)
\(\Rightarrow x=\dfrac{5}{2}\)
⇒ C
Bài 6:
\(\dfrac{3}{4}+\dfrac{1}{4}:x=2\)
\(\Rightarrow\dfrac{1}{4}:x=2-\dfrac{3}{4}\)
\(\Rightarrow\dfrac{1}{4}:x=\dfrac{5}{4}\)
\(\Rightarrow x=\dfrac{1}{4}:\dfrac{5}{4}\)
\(\Rightarrow x=\dfrac{1}{5}\)
⇒ D
Bài 4
\(\dfrac{-7}{15}\cdot\dfrac{5}{8}\cdot\dfrac{15}{-7}\cdot\left(-32\right)\\ =\dfrac{\left(-7\right).5.15.\left(-4\right).8}{15.8.\left(-7\right)}\\ =\dfrac{-20}{1}=-20\\ \Rightarrow C\)
Bài 5
\(2x+\dfrac{1}{2}=5\dfrac{1}{2}\\
\Rightarrow2x+\dfrac{1}{2}=\dfrac{11}{2}\\
\Rightarrow2x=\dfrac{11}{2}-\dfrac{1}{2}\\
\Rightarrow2x=5\\
\Rightarrow x=\dfrac{5}{2}\\
\Rightarrow C\)
Bài 6
\(\dfrac{3}{4}+\dfrac{1}{4}:x=2\\ \Rightarrow\dfrac{1}{4}:x=2-\dfrac{3}{4}\\ \Rightarrow\dfrac{1}{4}:x=\dfrac{8}{4}-\dfrac{3}{4}\\ \Rightarrow\dfrac{1}{4}:x=\dfrac{5}{4}\\ \Rightarrow x=\dfrac{1}{4}:\dfrac{5}{4}\\ \Rightarrow x=\dfrac{1}{4}\cdot\dfrac{4}{5}\\ \Rightarrow x=\dfrac{4}{20}\\ \Rightarrow x=\dfrac{1}{5}\\ \Rightarrow D\)
