In an industry, a cyclone collector with $80 \%$ efficiency is installed for air purification, followed by an electrostatic precipitator with $50 \%$ efficiency. The concentration of particles entering the cyclone collector is $10 \mathrm{~mg} / \mathrm{m}^{3}$.
The concentration (in $\mathrm{mg} / \mathrm{m}^{3}$) of particles exiting the precipitator is $\_\_\_\_$ (rounded off to two decimal places).
