Following bike

At 8:00 a.m., my son rode a bicycle at a speed of 18 km/h. at 8:20 a.m., his father followed him at a speed of 60 km/h. How long will it take for Dad to arrive?

Final Answer:

t =  8.6 min

Step-by-step explanation:

$$\begin{gathered} v_1=18\text{km/h} \\ {v}_2=60\text{km/h} \\ T=8:20-8:00 \\ T=20\text{min}\to \text{h}=20:60\text{h}=0.33333\text{h} \\ {s}_1=s_2 \\ {v}_1\cdot (x+T)=v_2\cdot x \\ 18\cdot (x+0.33333333333333)=60\cdot x \\ 42x=6 \\ x=\frac{6}{42}=0.14285714 \\ x=\frac{1}{7}\doteq 0.142857 \\ t=x\to \text{min}=x\cdot 60\text{min}=0.1429\cdot 60\text{min}=8.6\text{min}=8.6\text{min} \end{gathered}$$

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