The analysis process is as follows:

There are four story books and three science books in the library. Xiaohua wants to borrow one from each person, which is divided into two steps.

The first step is to borrow a story book. There are four options.

The second step is to borrow popular science books. There are three options.

So the total selection method =4×3= 12.

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