13.448 Two trains departed from station A with an interval of 12 min and almost immediately developed the same speed of 50 km/h. They are traveling in the same direction without stopping, maintaining the indicated speed unchanged. At what speed was the oncoming train traveling if it met these trains 5 min apart?
Solution. Let $x$ be the speed of the oncoming train. The distance between the other two trains is $50 \cdot \frac{1}{5}=10$ km. Therefore, the oncoming train met the second of these two trains after $\frac{10}{x+50}$ hours from meeting the first one.

$$
\text { According to the condition } \frac{10}{x+50}=\frac{1}{12} \Rightarrow x=70 \text {. }
$$

Answer: 70 km $/$ h.