[tex]Dane:\\t_1 = 0,5 \ h\\v_1 = 70\frac{km}{h}\\t_2 = 1,5 \ h\\v_2 = 100\frac{km}{h}\\t_3 = 0,75 \ h\\v_3 = 50\frac{km}{h}\\Szukane:\\v_{sr} = ?\\\\Rozwiazanie\\\\v_{sr} = \frac{s_{c}}{t_{c}}\\\\s_{c} = s_1+s_2+s_3\\\\s = v\cdot t\\\\s_{c} = v_1t_1+v_2t_2+v_3t_3 = (70\cdot0,5+100\cdot1,5+50\cdot0,75) \ km = 222,5 \ km\\\\t_{c} = t_1+t_2+t_3 = (0,5+1,5+0,75) \ h = 2,75 \ h\\\\v_{sr} = \frac{222,5 \ km}{2,75 \ h}\\\\\boxed{v_{sr} = 80,(90)\frac{km}{h} \approx80,91\frac{km}{h}}[/tex]
