How many ways can 5 people be seated in 5 seats?

How many ways can 5 people be seated in 5 seats?

We have the permutation 5!.

Because the first seat can have 5 different people.
The next seat has 5 - 1 = 4 people since one person is in the first seat
The next seat can have 5 - 2 = 3 people since we have two people in the first two seats
The next seat can have 5 - 3 = 2 people since we have three people in the first three seats
The next seat can have 5 - 4 = 1 people since we have four people in the first four seats

Type in 5! into our search engine, and we get 120.