## 191. Math Puzzle $4 / 81$

Sound waves travel through the air at a speed of about $340 \mathrm{~m}$ per second, while radio waves travel at about $300000 \mathrm{~km}$ per second.

Who hears the speaker first:

a listener in the first row in the hall, sitting two meters away from the speaker, or a radio listener following the broadcast over headphones from a distance of $1000 \mathrm{~km}$?
Since sound waves travel approximately $340 \mathrm{~m}$ per second in the air, they need $\frac{1}{170}$ seconds to travel the two meters to the listener in the hall, because:

$$
t_{1}=\frac{2 \mathrm{~m} \cdot 1 \mathrm{~s}}{340 \mathrm{~m}}=\frac{2}{340} \mathrm{~s}=\frac{1}{170} \mathrm{~s}
$$

Radio waves, which travel approximately $300000 \mathrm{~km}$ per second, need $\frac{1}{300}$ seconds to reach the radio listener who is $1000 \mathrm{~km}$ away, because

$$
t_{2}=\frac{1000 \mathrm{~km} \cdot 1 \mathrm{~s}}{300000 \mathrm{~km}}=\frac{1}{300} \mathrm{~s}
$$

Therefore, the radio listener can hear the speaker earlier than the listener in the hall.