Let's say that you are arranging them from left to right.
You have 4 choices for the first book, then 3 choices for the next book, then 2 choices, then only 1 choice.
To find the total number of choices, multiply these numbers: 4x3x2x1 = 24 different ways.
(A short way to write 4x3x2x1 is 4!, where "!" means "factorial".)
Let's say that you are arranging them from left to right.
You have 4 choices for the first book, then 3 choices for the next book, then 2 choices, then only 1 choice.
To find the total number of choices, multiply these numbers: 4x3x2x1 = 24 different ways.
(A short way to write 4x3x2x1 is 4!, where "!" means "factorial".)