Most tested (2020-2024):

1. Sum of series with general term (decomposition into standard sums)
2. AP/GP with conditions (find terms, common difference/ratio)
3. Infinite GP sum
4. Telescoping series
5. AM-GM optimization

Difficulty distribution:

• 40% medium (direct formula application)
• 40% hard (multi-step, AGP, conditions)
• 20% easy $\frac{basic AP}{GP computation}$

Time targets:

• Basic AP/GP: 1-2 minutes
• Series decomposition: 2-3 minutes
• AGP/complex telescoping: 3-4 minutes
• AM-GM optimization: 2-3 minutes