2. Variant 1.

Athletes started in groups of 3 people with a delay between groups of several seconds. Petya, Vasya, and Kolya started simultaneously, and they were in the seventh trio from the beginning and the fifth trio from the end. How many athletes participated in the race?
Answer: 33.

Solution. After Petya, Kolya, and Vasya started, 4 more triples of athletes started. Then the total number of triples was $7+4=11$, i.e., a total of 33 athletes participated in the race.