Question

Bài 1: Tìm x biết

a) \(\dfrac{5}{6}\) : x = 30:3

b) x : 2,5 = 0,003:0,75

c) 3,8 : (2x) = \(\dfrac{1}{4}\) : 2\(\dfrac{2}{3}\)

d) \(\dfrac{2}{3}\) : 0,4 = x : \(\dfrac{4}{5}\)

f) 3\(\dfrac{4}{5}\) : 40\(\dfrac{8}{15}\) = 0,25 : x

e) \(\dfrac{x}{-15}\) = \(\dfrac{-60}{x}\)

Answer 1

a) \(\dfrac{5}{6}:x=30:3\)

\(\Leftrightarrow\dfrac{5}{6}:x=10\)

\(\Leftrightarrow x=\dfrac{5}{6}:10\)

\(\Leftrightarrow x=\dfrac{1}{12}\)

Vậy .......

b) \(x:2,5=0,003:0,75\)

\(\Leftrightarrow x:2,5=0,004\)

\(\Leftrightarrow x=0,004.2,5\)

\(\Leftrightarrow x=0,01\)

Vậy .......

c) \(3,8:\left(2x\right)=\dfrac{1}{4}:2\dfrac{2}{3}\)

\(\Leftrightarrow3,8:\left(2x\right)=\dfrac{1}{4}:\dfrac{8}{3}=\dfrac{3}{32}\)

\(\Leftrightarrow2x=3,8:\dfrac{3}{32}\)

\(\Leftrightarrow2x=\dfrac{698}{25}\)

\(\Leftrightarrow x=\dfrac{304}{15}\)

Vậy ...

d) \(\dfrac{2}{3}:0,4=x:\dfrac{4}{5}\)

\(\Leftrightarrow x:\dfrac{4}{5}=\dfrac{2}{3}\)

\(\Leftrightarrow x=\dfrac{8}{15}\)

Vậy ....

e) \(3\dfrac{4}{5}:40\dfrac{8}{15}=0,25:x\)

\(\Leftrightarrow0,25:x=\dfrac{19}{5}:\dfrac{608}{15}\)

\(\Leftrightarrow0,25x=\dfrac{57}{608}\)

\(\Leftrightarrow x=\dfrac{228}{608}\)

Vậy ...

e) \(\dfrac{x}{-15}=\dfrac{-60}{x}\)

\(\Leftrightarrow xx=\left(-60\right)\left(-15\right)\)

\(\Leftrightarrow x^2=900\)

\(\Leftrightarrow\left[{}\begin{matrix}x^2=30^2\\x^2=\left(-30\right)^2\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=30\\x=-30\end{matrix}\right.\)

Vậy ...

Answer 2

Answer 3