1. The Winter Olympics is held every four years, and this year is the 24th Winter Olympics. This is about the knowledge of arithmetic progression in mathematics;

2. There are 7 major events in this Beijing Winter Olympics, 15 event and 109 event. This is about the knowledge of classification and set in mathematics;

3. In the U-pool competition, five referees scored points after the snowboarders slid, and the highest and lowest points were removed from the calculation. This is the knowledge about the average in mathematics.