Question

In how may different ways can you put 4 books on a shelf ?

Answer 1

You can put 4 books in

4!
= (4)(3)(2)(1)
= 24 different ways

(It is called Four factorial)

Answer 2

For this, we have a new concept. Its factorial.
n ! = (n -1) (n-2) (n-3)...(1)

Here, the books can be arranged in 4! Ways i.e. 4×3×2×1 = 24 different ways.