Theo bài ra, ta có:
`x/2=y/3`
$⇒\dfrac{x}{10}=\dfrac{y}{15}(1)$
`y/5=z/7`
$⇒\dfrac{y}{15}=\dfrac{z}{21}(2)$
Từ $(1),(2)⇒\dfrac{x}{10}=\dfrac{y}{15}=\dfrac{z}{21}$
Áp dụng ...
$\dfrac{x}{10}=\dfrac{y}{15}=\dfrac{z}{21}=\dfrac{x+y+z}{10+15+21}=\dfrac{138}{46}=3$
$\dfrac{x}{10}=3⇒x=3.10=30$
$\dfrac{y}{15}=3⇒y=3.15=45$
$\dfrac{z}{21}=3⇒z=3.21=63$