The arrangement a (n, m) = n× (n- 1). (n-m+ 1) = n！ /(n-m)！ (n is subscript and m is superscript, the same below)
Combination C(n, m)=P(n, m)/P(m, m) =n! /m！ (n-m)！ ;
For example:
A(4，2)=4！ /2! =4*3= 12
C(4，2)=4！ /(2! *2! )=4*3/(2* 1)=6
Second, the difference between c and p in probability:
1 means different.
C stands for combination, such as A, B and C. There are three ways to take out two people to participate in activities, namely A, B, C and B, which are not sequential, but only combination.
P stands for arrangement method, which means to arrange some objects in order. What is the general method?
2. Different in nature
Formula P refers to arrangement, and R elements are selected from N elements for arrangement (i.e. sorting).
Formula C refers to combination, in which R elements are taken from N elements without arrangement (that is, without sorting).
Extended data
In the early stage of the development of probability theory, people noticed that it is not enough for classical probability to consider only a limited number of test results, but also an infinite number of test results. For this reason, an infinite number of test results can be represented by a certain region S in Euclidean space, and the test results have the so-called "uniform distribution" property. The precise definition of "uniform distribution" is similar to the concept of "equal possibility" in classical probability theory.
It is assumed that the area S and any small area A that may appear in it are measurable, and the measured size is expressed by μ(S) and μ(A) respectively. For example, the length of one-dimensional space, the area of two-dimensional space and the volume of three-dimensional space. Suppose this metric has various attributes, such as length, such as nonnegativity and additivity.
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