c(m+n- 1,m)×p^n×( 1-p)^m。 Is to take out m different elements (0≤m≤n) from n different elements at a time, and combine them into a group in no particular order, which is called the combination of selecting m elements from n elements without repetition. The sum of all these combinations is called the number of combinations.
Extended data:
You can repeatedly select m elements from n different elements. Synthesizing a group of m elements called n elements regardless of their order is a repeatable combination. Two repeated combinations are the same if and only if the elements are the same and the same elements are taken the same times.
The calculation method of permutation and combination is as follows:
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)！ .