Homework is an indispensable basic link in classroom teaching, an important link in the consolidation of knowledge after class, and an important way for students to understand knowledge, digest knowledge, and improve their problem-solving ability. In the practice of mathematics teaching in primary schools, attention should be paid to the effectiveness of homework assignments in different links before, during and after class, and the content of homework should take into account the reality of students at different levels. This paper expounds the strategy of hierarchical design of mathematics homework from the aspects of the hierarchical design and arrangement of mathematics homework in the upper grades of primary school, aiming to effectively improve the quality of mathematics classroom teaching in the upper grades of primary school.

The COVID-19 crisis, which occurred in 2020, brought crisis events back to the attention of scholars. With the increasing frequency of crisis events, the influence of crisis events on stock markets has become more obvious. This paper focuses on the impact of the subprime crisis, the Chinese stock market crash crisis and the COVID-19 crisis on the volatility and risk of the world’s major stock markets. In this paper, we first fit the volatility using EGARCH model and detect asymmetry of volatility. After that, a VaR model is calculated on the basis of EGARCH to measure the impact of the crisis event on the risk of stock markets. This paper finds that the subprime crisis has a significant influence on the risk of the stock market in China, US, South Korea, and Japan. During the COVID-19 crisis, there was little change in the average risk of each country. But at the beginning of the COVID-19 crisis, there was a significant increase in the risk of each country’s stock market. The Chinese stock market crash crisis had a more pronounced effect on the Chinese and Japanese stock markets and a lesser effect on the US and Korean stock markets.

Innovation in teaching models is a basic requirement of the Ministry of Education for schools. If a school wants to achieve development, it cannot adhere to traditional rigid teaching models. At the same time, innovating teaching models is also an important requirement for improving education and teaching effectiveness. Through innovation in teaching models, the inherent drawbacks of the current teaching model can be removed and the classroom teaching effect can be better played. The rapidly developing internet era provides unprecedented development opportunities for innovative teaching models. Schools should establish internet learning platforms to encourage students to actively and independently participate in online learning. This paper discusses the classroom teaching model in vocational colleges under the background of "Internet plus", and how it serves our daily teaching activities.