Lời giải:
$\frac{x}{10}=\frac{y}{5}\Rightarrow \frac{x}{20}=\frac{y}{10}$
$\frac{y}{2}=\frac{z}{3}\Rightarrow \frac{y}{10}=\frac{z}{15}$
$\Rightarrow \frac{x}{20}=\frac{y}{10}=\frac{z}{15}$
Áp dụng TCDTSBN:
$\Rightarrow \frac{x}{20}=\frac{y}{10}=\frac{z}{15}=\frac{4z}{60}=\frac{x+4z}{20+60}=\frac{320}{80}=4$
$\Rightarrow x=20.4=80; y=10.4=40; z=15.4=60$