Odpowiedź:
80 km - połowa
[tex]v = \frac{s}{t}[/tex]
[tex]t = \frac{s}{v}[/tex]
[tex]V_{sr} = \frac{\sum {s}}{\sum t}[/tex]
[tex]V_{sr} = \frac{s_{1} + s{2}}{\frac{s_{1}}{v_{1}}+\frac{s_{2}}{v_{2}}}[/tex]
[tex]V_{sr} = \frac{80+80}{\frac{80}{100}+\frac{80}{40}} = \frac{160}{0,8 + 2} = \frac{160}{2,8}[/tex]
[tex]V_{sr} = 57,14286 \ \frac{km}{h}[/tex]