13.394 Two brothers had tickets to a stadium located 10 km from their home. At first, they planned to walk to the stadium, but they changed their mind and decided to use a bicycle, agreeing that one would go by bicycle while the other would walk at the same time. After covering part of the distance, the first brother would leave the bicycle, and the second, upon reaching the abandoned bicycle, would ride it and catch up with the first at the stadium entrance. How much time do the brothers save with this plan compared to their initial intention of walking the entire distance, if each of them on a bicycle covers each kilometer 12 minutes faster than on foot?
Solution. Since the brothers arrived at the stadium simultaneously (i.e., spent the same amount of time on the journey), they walked (and cycled) the same distance. But in total, they walked 10 km, so each of them walked 5 km. Therefore, the time gain will be $5 \cdot 12=60$ minutes.

Answer: 1 hour.