What if we have the eight books...  But, we can only put three of them on the shelf?  How many arrangements are possible?

Let's figure it out!

** It's ALWAYS better to think than to just try to slam through a memorized formula!

Here are the books and the slots:

A  B  C  D  E  F  G  H


__  __  __
How many choices do we have for this slot?

8  __  __
Let's say we put book C in slot 1...  How many choices are left?

8 * 7  __
How many are left?

8 * 7 * 6 = 336

That wasn't bad at all!



If you have 10 books and you want to arrange 4 of them on a bookshelf, how many ways can you do it?