## 166. Math Puzzle $3 / 79$

Frank needs four minutes to cover the $300 \mathrm{~m}$ to the street corner, then runs $50 \mathrm{~m}$ up the stairs in five minutes, and completes the remaining $600 \mathrm{~m}$ of the journey in ten minutes.

What is his average speed?

Can he be considered a "fast walker" if we allow him double the time for the stairs compared to a normal walking pace, relative to the general average walking speed for pedestrians ( $5 \frac{\mathrm{km}}{\mathrm{h}}$ )?
The average speed $v$ is determined from the total distance traveled ( $s=$ $950 \mathrm{~m}$ ) and the time required ( $t=19 \mathrm{~min}$ ).

$$
v=\frac{950 \mathrm{~m}}{19 \mathrm{~min}}=50 \frac{\mathrm{m}}{\mathrm{min}}
$$

Frank covered an average of $50 \mathrm{~m}$ per minute on his way to school, which would be 3000 $\mathrm{m}$ in an hour. Therefore, his average speed is $3 \mathrm{~km} / \mathrm{h}$, which is a rather slow pace compared to the general $5 \mathrm{~km} / \mathrm{h}$ for pedestrians.

But who knows how many streets he has to cross on his way to school.