Question

[Hương Đỗ]

Giúp mik với ạ! mik đang cần gấp!

Bài 2: 

a) Tìm tỉ số \(\dfrac{x}{y}\) biết \(\dfrac{2x-y}{x+y}\) =\(\dfrac{2}{7}\) 

b) Biết \(\dfrac{x}{y}\)=\(\dfrac{2}{3}\); \(\dfrac{t}{y}\)=\(\dfrac{4}{9}\); \(\dfrac{z}{t}\)=\(\dfrac{5}{8}\) . Tìm tỉ số \(\dfrac{x}{z}\)

Answer 1

[Lê Song Phương]

a) Có \(\dfrac{2x-y}{x+y}=\dfrac{2}{7}\) 

\(\Leftrightarrow7\left(2x-y\right)=2\left(x+y\right)\)

\(\Leftrightarrow14x-7y=2x+2y\)

\(\Leftrightarrow12x=9y\)

\(\Leftrightarrow\dfrac{x}{y}=\dfrac{9}{12}=\dfrac{3}{4}\)

b) Ta có \(\dfrac{t}{y}=\dfrac{4}{9}\) và \(\dfrac{z}{t}=\dfrac{5}{8}\)

\(\Rightarrow\dfrac{t}{y}.\dfrac{z}{t}=\dfrac{4}{9}.\dfrac{5}{8}\)

\(\Leftrightarrow\dfrac{z}{y}=\dfrac{5}{18}\)

\(\Leftrightarrow\dfrac{y}{z}=\dfrac{18}{5}\)

Lại có \(\dfrac{x}{y}=\dfrac{2}{3}\)

\(\Rightarrow\dfrac{x}{y}.\dfrac{y}{z}=\dfrac{2}{3}.\dfrac{18}{5}\)

\(\Leftrightarrow\dfrac{x}{z}=\dfrac{12}{5}\)