Question

Tìm số thích hơp cho ?:

a) \(\dfrac{3}{16}:\dfrac{?}{8}=\dfrac{3}{4};\)

b) \(\dfrac{1}{25}:\dfrac{-3}{?}=\dfrac{-1}{15};\)

c) \(\dfrac{?}{12}:\dfrac{-4}{9}=\dfrac{-3}{16}.\)

Answer 1

\(a.\)

\(\dfrac{3}{16}:\dfrac{?}{8}=\dfrac{3}{4}\)

\(\Leftrightarrow\dfrac{3}{16}\cdot\dfrac{8}{?}=\dfrac{3}{4}\)

\(\Leftrightarrow\dfrac{3}{2?}=\dfrac{3}{4}\)

\(\Leftrightarrow?=2\)

\(b.\)

\(\dfrac{1}{25}:-\dfrac{3}{?}=-\dfrac{1}{15}\)

\(\Leftrightarrow\dfrac{1}{25}\cdot\dfrac{-?}{3}=-\dfrac{1}{15}\)

\(\Leftrightarrow\dfrac{-?}{75}=-\dfrac{1}{15}\)

\(\Leftrightarrow?=\dfrac{75}{15}=5\)

\(c.\)

\(\dfrac{?}{12}:-\dfrac{4}{9}=-\dfrac{3}{16}\)

\(\Leftrightarrow\dfrac{?}{12}\cdot\dfrac{-9}{4}=-\dfrac{3}{16}\)

\(\Leftrightarrow\dfrac{-3?}{16}=-\dfrac{3}{16}\)

\(\Leftrightarrow?=1\)

 

Answer 2

Mk gọi ? = x nha

a) \(\dfrac{3}{16}:\dfrac{x}{8}=\dfrac{3}{4}\)  

             \(\dfrac{x}{8}=\dfrac{3}{16}:\dfrac{3}{4}\) 

             \(\dfrac{x}{8}=\dfrac{1}{4}\)

⇒\(x=\dfrac{1.8}{4}=2\) 

b) \(\dfrac{1}{25}:\dfrac{-3}{x}=\dfrac{-1}{15}\) 

             \(\dfrac{-3}{x}=\dfrac{1}{25}:\dfrac{-1}{15}\) 

             \(\dfrac{-3}{x}=\dfrac{-3}{5}\) 

⇒x=5

c) \(\dfrac{x}{12}:\dfrac{-4}{9}=\dfrac{-3}{16}\) 

            \(\dfrac{x}{12}=\dfrac{-3}{16}.\dfrac{-4}{9}\) 

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

⇒x=1