3. 31 cars started simultaneously from one point on a circular track: the first car at a speed of 61 km/h, the second at 62 km/h, and so on (the 31st at 91 km/h). The track is narrow, and if one car overtakes another by a full lap, they crash into each other, both fly off the track, and are eliminated from the race. In the end, only one car remained. At what speed is it traveling?
Solution. First, the fastest car collides with the slowest, then the second fastest collides with the second slowest, and so on. In the end, the car with the median speed remains, i.e., the 16th. It travels at a speed of $76 \mathrm{Km} /$ h.

Criteria. Full solution - 7 points.

Solution that correctly describes the overall sequence of collisions but with an incorrect answer in the count - 6 points.

Correct answer + cars that have been eliminated are written out and crossed out, but the principle (order of elimination) is not explained - 4 points.