Question

Mike is picking out 4 books to read out of collection of 12. How many ways can the books be picked?

Answer 1

3 sets or it you could divide which would still give you 3

Answer 2

You have to choose 4 books out of 12 books. You can choose any 4 books.

You can do that in 12C4 ways.


`{}^(12) C_4 = (12!)/(4! * (12 - 4)!) \\ \\ = (12!)/(4! * 8!) \\ \\ = (12 * 11 * 10 * 9)/(4 * 3 * 2 * 1) \\ \\ = 495 \\`

You can choose 4 books in 495 ways.