$\text{Ta có: $\dfrac{x}{y}$ = $\dfrac{7}{20}$ $\Leftrightarrow$ $\dfrac{x}{7}$ = $\dfrac{y}{20}$ (1)}$
$\text{$\dfrac{y}{z}$ = $\dfrac{5}{8}$ $\Leftrightarrow$ $\dfrac{y}{5}$ = $\dfrac{z}{8}$ $\Rightarrow$ $\dfrac{y}{20}$ = $\dfrac{z}{32}$ (2)}$
$\text{Từ (1) (2) $\Rightarrow$ $\dfrac{x}{7}$ =$\dfrac{y}{20}$ = $\dfrac{z}{32}$ $\Rightarrow$ $\dfrac{2x}{14}$ = $\dfrac{5y}{100}$ = $\dfrac{22}{64}$}$
$\text{Áp dụng tính chất DTSBN}$
$\text{$\dfrac{2x}{14}$ = $\dfrac{5y}{100}$ =$\dfrac{2z}{64}$ $\Rightarrow$ $\dfrac{2x+5y-2z}{14+100-64}$ = $\dfrac{100}{50}$ =2}$
$\text{$\Rightarrow$ $\dfrac{2x}{14}$=2 $\Rightarrow$ $\dfrac{x}{7}$ =2 $\Rightarrow$ x=14}$
$\text{$\Rightarrow$ $\dfrac{5y}{100}$=2 $\Rightarrow$ $\dfrac{y}{20}$ =2 $\Rightarrow$ y=40}$
$\text{$\Rightarrow$ $\dfrac{2z}{64}$=2 $\Rightarrow$ $\dfrac{z}{32}$ =2 $\Rightarrow$ z=64}$
$\text{Vậy x=14; y=40; z=64}$
