The cyclist

The cyclist drove from A to B, 60 km away. The first half drove at 30km/h, the second at 20km/h. How long did it take for him?

Correct answer:

t =  2.5 h

Step-by-step explanation:

$$\begin{gathered} s=60\text{ km } \\ {v}_1=30\text{ km/h } \\ {v}_2=20\text{ km/h } \\ {s}_1=s\mathrm{/}2=60\mathrm{/}2=30\text{ km } \\ {t}_1=s_1\mathrm{/}{v}_1=30\mathrm{/}30=1\text{ h } \\ {t}_2=s_1\mathrm{/}{v}_2=30\mathrm{/}20={\displaystyle \frac{3}{2}}=1.5\text{ h } \\ t=t_1+t_2=1+1.5=2.5\text{ h} \end{gathered}$$

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