The tourist

A man travelled a distance of 61 km in 9 hours. He travelled partly on foot at 4 km/h and partly by bicycle at 9 km/h.
Find the distance travelled on foot.

Final Answer:

s₁ =  16 km

Step-by-step explanation:

$$\begin{gathered} s=61\text{km} \\ t=9\text{h} \\ {v}_1=4\text{km/h} \\ {v}_2=9\text{km/h} \\ s=s_1+s_2 \\ s=v_1\cdot t_1+v_2\cdot (t-t_1) \\ s=v_1\cdot t_1+v_2\cdot (t-t_1) \\ 61=4\cdot t_1+9\cdot (9-t_1) \\ 5t_1=20 \\ {t}_1=\frac{20}{5}=4 \\ {t}_1=4 \\ {s}_1=v_1\cdot t_1=4\cdot 4=16\text{km} \end{gathered}$$

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