2 Simple calculation (required)

3, engineering problems (when necessary)

4. Concentration problem

5. Travel issues (including meetings, back-to-back, catching up) (required)

6. Graphic problems (a mixture of triangles, squares, circles, sectors, etc. ) (required)

7. Digital fan

8. Indefinite equation

9. The principle of pigeon nest

10, cattle grazing problem

1 1. Scale problem (some graphics, engineering and travel problems can be solved by scale) (required)

12, exclusion principle