2. Two balls, the sizes of which can be neglected in this problem, move along a circle. When moving in the same direction, they meet every 20 seconds, and when moving in opposite directions - every 4 seconds. It is known that when moving towards each other along the circle, the distance between the approaching balls decreases by 75 cm every 3 seconds (until they meet). Find the speed of the slower ball (in cm/sec).
# Solution:

Let the speed of the faster ball be $v$, and the slower one be $u$. When moving in the same direction, the faster ball catches up with the slower one when the difference in the distances they have traveled equals the length of the circle. According to the problem, we set up a system of two linear equations.

$$
\left\{\begin{array}{l}
(u+v) \cdot 4=(v-u) \cdot 20 \\
(u+v) \cdot 3=75
\end{array} . \text { From which } u=\frac{2}{3} v, v=15 \text{ cm/s }; u=10 \text{ cm/s}\right.
$$

Answer: 10.