Arrangement formula: A(n, m) = n× (n-1) ... (n-m+1) = n! /(n-m)！ (n is subscript and m is superscript, the same below). The formula of combination: C(n, m)=P(n, m)/P(m, m) =n! /m！ ×(n-m)！ .

Permutation and combination, before permutation, the first concept we want to talk about is "permutation", and the English word for permutation is Permutation or Arrangement, so in mathematical symbols, either P or A can be used, and the two meanings are exactly the same. Our common p will be followed by two numbers (or letters) to the right, the number n in the lower right corner represents the total number, and the number m in the upper right corner represents the drawn number.

permutation and combination

Permutation and combination is the most basic concept of combinatorics. The so-called arrangement refers to taking out a specified number of elements from a given number of elements for sorting. Combination refers to taking out only a specified number of elements from a given number of elements, regardless of sorting. The central problem of permutation and combination is to study the total number of possible situations in a given permutation and combination. Permutation and combination are closely related to classical probability theory.

Definition of arrangement: from N different elements, arbitrarily choose m(m≤n, m and n are natural numbers, the same below) to arrange in a column in a certain order, which is called an arrangement of taking M elements from N different elements; All permutation numbers of m(m≤n) elements from n different elements are called permutation numbers of m elements from n different elements.

Refer to the above content: Baidu Encyclopedia-permutation and combination