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Average score of second grade mathematics book 2
Seven kinds of division.

Analysis process:

18 = 2x9 = 6x3 = 9x2 =18x1or 9X2=3X6, a * * *, there are seven kinds of division methods.

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)! ;

For example:

A(4,2)=4! /2! =4*3= 12

C(4,2)=4! /(2! *2! )=4*3/(2* 1)=6