Answer: 10.

It is clear that all buses from Moscow will meet the same number of buses from Orel, and we can assume that a bus from Moscow departed at 12:00. It is easy to understand that it will meet buses that left Orel at $7:30, 8:30, \ldots, 15:30, 16:30$ and only them. There are 10 such buses.

$\pm$ Correct reasoning with an arithmetic error leading to an incorrect answer. 4-5 points

Ғ Frequency of encounters (every half hour) has been calculated, but the answer is incorrect. 3 points

- Correct answer without explanation. 1 point
1. Buses from Moscow to Oryol depart at the beginning of each hour (at 00 minutes). Buses from Oryol to Moscow depart in the middle of each hour (at 30 minutes). The journey between the cities takes 5 hours. How many buses from Oryol will the bus that left from Moscow meet on its way?