$\dfrac{x}{5}$= $\dfrac{y}{6}$; $\dfrac{y}{8}$ = $\dfrac{z}{7}$ $ và x+y-z=69$
$\dfrac{x}{5}$= $\dfrac{y}{6}$ = $\dfrac{x}{5.4}$= $\dfrac{y}{6.4}$ = $\dfrac{x}{20}$= $\dfrac{y}{24}$
$\dfrac{y}{8}$ = $\dfrac{z}{7}$ = $\dfrac{y}{8.3}$ = $\dfrac{z}{7.3}$ = $\dfrac{y}{24}$ = $\dfrac{z}{21}$
⇒ $\dfrac{x}{20}$= $\dfrac{y}{24}$= $\dfrac{z}{21}$ = $\dfrac{ x+y-z}{20+24-21}$ = $\dfrac{69}{23}$ $=3 $
$\dfrac{x}{20}$$=3 ⇒ x =3.20 = 60$
$\dfrac{y}{24}$$= 3 ⇒ y = 3.24 = 72$
$\dfrac{z}{21}$ $= 3 ⇒ z = 3.21 = 63 $
