Tourists

The first group of tourists started from the cottage at 7:00 AM at a speed of 4 km/h. The second started after them 21 minutes later at a 6 km/h. How long and how many kilometers from the cottage will catch the first group?

Correct answer:

t =  0.7 h
s =  4.2 km

Step-by-step explanation:

$$\begin{gathered} v_1=4\text{km/h} \\ {v}_2=6\text{km/h} \\ {t}_2=21\text{min}\to \text{h}=21:60\text{h}=0.35\text{h} \\ {s}_1=s_2=s \\ {v}_1\cdot (t+t_2)=v_2\cdot t \\ 4\cdot (t+0.35)=6\cdot t \\ 2t=1.4 \\ t=\frac{1.4}{2}=0.7 \\ t=\frac{7}{10}=0.7=0.7\text{h} \end{gathered}$$

$s=v_2\cdot t=6\cdot 0.7=4.2\text{km}$

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