C represents the number of combination methods.

For example, c (3,2) means to select two objects from three objects, total * * *, and there are three methods, namely, A, B and C (three objects are different at the same time).

2, the calculation formula of a:

A indicates the number of arrangement methods.

For example: n different objects, to take out m (m

You can also think of it this way: the first one has n choices, the second one has n- 1 choices, the third one has n-2 choices, and the m-th one has n+ 1-m choices, so the total * * arrangement method is n (n-65438+).

Difference:

Mathematical probability a formula (permutation): a (superscript m, subscript n)=n right) =n! /(n-m)！ , c formula (combination): c (superscript m, subscript n)=n right) =n! /[m！ (n-m)！ ]。

Formula A is the number of permutation methods, which has nothing to do with order, and formula C is the number of combination methods, which has nothing to do with order.

Arrangement: from N different elements, any m(m≤n, m and n are natural numbers, the same below) different elements are arranged in a column in a certain order, which is called the arrangement of taking out M elements from N different elements; All permutation numbers of m(m≤n) elements taken from n different elements are called permutation numbers of m elements taken from n different elements, which are represented by symbol A(n, m).

Combination: take any m(m≤n) elements from n different elements to form a group, which is called the combination of m elements of n different elements; The number of all combinations of m(m≤n) elements from n different elements is called the number of combinations of m elements from n different elements. Represented by the symbol C(n, m).