In any arrangement, if the order is the matter, then we should multiply the numbers of the arrangement by decreasing until reach 1
Since there are 8 students, then
The 1st one has 8 choices
The 2nd one has 7 choices
The 3rd one has 6 choices
The 4th one has 5 choices
The 5th one has 4 choices
The 6th one has 3 choices
The 7th one has 2 choices
The 8th one has 1 choice
Then the total number of choices = 8 x 7 x 6 x 5 x 4 x 3 x 2 x 1 = 40,320
We calle