Question

I need help

You find 20 books that you checked out from the library as you are cleaning your room. You need to take 4 books back to the library, and you want to set them aside in a pile on your desk.  


How many ways can 4 of the 20 books be arranged in a pile?

Answer 1

the answer is 20P4 = 4845

Explanation:

Answer 2

There are 20 ways to pick the first book, 19 ways for the second

Explanation:

If order of the 4 books does not matter then

₂₀C₄ = 20! / (20-4)!4! = 20!/(16!*4!) = 4845 ways