The speed of the train can be easily determined by every passenger: They measure how many seconds it takes to cover $200 \mathrm{~m}$! (There are distance markers every 200 meters along the track.) If this number of seconds is $p$, then the train is traveling at a speed of $\frac{720}{p} \mathrm{~km}$ per hour. Is this calculation correct?
A $\frac{200}{p} \mathrm{~m} / \mathrm{sec}$ speed needs to be converted to km/h units.

$$
1 \mathrm{~m} / \mathrm{sec}=\frac{1}{1000} \mathrm{~km} / \frac{1}{3600} \text { hour }=\frac{3600}{1000} \mathrm{~km} / \text { hour }=3.6 \mathrm{~km} / \text { hour, }
$$

and thus

$$
\frac{200}{p} \mathrm{~m} / \mathrm{sec}=3.6 \frac{200}{\mathrm{p}} \mathrm{km} / \text { hour }=\frac{720}{\mathrm{p}} \mathrm{km} / \text { hour. }
$$

Therefore, the calculation is correct.

Weisz Edit (Bp., V., Spinning, Weaving, and Knitting Technology II. o. t.)