[tex]\displaystyle\\
\frac{1}{2}\times \Big(\frac{1}{2}\times \Big(\frac{1}{2}\times 320 \Big)\Big ) = \\\\ \\
=\frac{1}{2}\times \frac{1}{2}\times \frac{1}{2}\times 320 = \\\\ \\
=\frac{1}{2^3}\times 320 = \frac{320}{2^3}=\frac{320}{8}=\boxed{40}
[/tex]
