Together 81559

A car drives for an hour on the highway at a speed of 100 km/h, then for half an hour at a speed of 80 km/h, and for another half hour in the field at a speed of 20 km/h. What track did he run together? What is the average speed of the car?

Correct answer:

s =  150 km
v =  75 km/h

Step-by-step explanation:

$$\begin{gathered} v_1=100\text{km/h} \\ {t}_1=1\text{h} \\ {v}_2=80\text{km/h} \\ {t}_2=1/2=\frac{1}{2}=0.5\text{h} \\ {v}_3=20\text{km/h} \\ {t}_3=1/2=\frac{1}{2}=0.5\text{h} \\ {s}_1=v_1\cdot t_1=100\cdot 1=100\text{km} \\ {s}_2=v_2\cdot t_2=80\cdot 0.5=40\text{km} \\ {s}_3=v_3\cdot t_3=20\cdot 0.5=10\text{km} \\ s=s_1+s_2+s_3=100+40+10=150\text{km} \end{gathered}$$

$$\begin{gathered} t=t_1+t_2+t_3=1+0.5+0.5=2\text{h} \\ v=\frac{s}{t}=\frac{150}{2}=75\text{km/h} \end{gathered}$$

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