This is a complete arrangement in which three elements are randomly selected from three elements and arranged in a certain order.

Let three external elements be 1, 2, 3 respectively.

There are six cases of * * *: 123,132,213,231,312,321.

That is 3x2x 1=6.

It can also be understood that taking three elements is divided into three steps. The first element * * * has three methods, the second * * * has two methods, and the third * * * has 1 method. According to the principle of multiplication, * * has 6 ways: 3x2x1=.