Simple arrangement
When two numbers are arranged, the positions of the two numbers can be interchanged; When two of the three numbers are arranged into two digits, let each number be the tenth digit (except 0), and other numbers are combined with it in turn. Simple combination
When solving the combination problem, we should think in a certain order, so that all the combinations can be listed, and we can think about solving the problem with the help of intuitive contact methods.
Function:
Permutation and combination is an important way of thinking in the counting part of follow-up extracurricular training. Classification step by step, the principle of addition, subtraction, multiplication and division, and then the application of permutation and combination numbers. First of all, we must understand the permutation problem, and the distinction of combination problems depends on whether it is related to sequence numbers.
The counting part in the early junior middle school includes geometric counting and digital counting, both of which use the idea of permutation and combination. Collocation is enlightenment, so we should pay attention to it.