The four operations of 1 and multiple digits are very complicated, and a problem needs to be calculated many times. One wrong step and the whole problem will be wrong.

2. The application problems in the lower grades are relatively simple, and most subjects are based on real life, so students are familiar with them and easy to understand; The application problems in Grade Three are very complicated, and the subject matter extends to other fields such as production and circulation, which makes students feel strange and difficult to understand.