The eighth unit of the first volume of the second grade mathematics of People's Education Press belongs to the wide-angle category of mathematics. This unit mainly studies the relatively simple content of permutation and combination, which permeates the mathematical thought of permutation and combination. Let students gradually cultivate the consciousness of orderly and comprehensive thinking in the process of exploring the law of arrangement and combination.

The teaching difficulty of this unit is that only by understanding the orderly arrangement and combination can we achieve neither repetition nor omission. However, in the process of students' study and practice, it is found that students are easily confused about permutation and combination in real life problems, which requires students to understand the concept of permutation and combination, master the problem-solving ideas and answering skills of permutation and combination, and optimize, consolidate and improve them through certain exercises.

Practice is an effective way to get familiar with methods, form experience, improve skills and consolidate knowledge. Unit exercises focus on students' understanding and application of this chapter. The unit test paper mainly stimulates students' adaptability to new knowledge through diversified test questions.