The analysis process is as follows:

Three students, A, B and C, line up, with A first. There are three options for A's position.

B is next, and there are two choices for the position of B.

Finally, row C. Except for the positions of rows A and B, row C has only 1 options. ..

From this, we can get: exclusion method =3×2× 1=6.

Extended data:

To do one thing, it needs to be divided into n steps. There are m 1 different methods to do the first step, m2 different methods to do the second step, ... and mn different methods to complete the n step. So * * * is N=m 1×m2×m3×…×mn to accomplish this? Different methods. And addition principle are the basic principles of mathematical probability.

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