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Here are the five books:
Let's use slots like we did with
the license plates:
We'll fill each slot -- one at a
time... Then we can use the counting principle!
The first slot:
We have all
5
books to choose from to fill this slot.
Let's say we put book C there...
Now, we only have
4
books that can go here...
How many books are left for this
slot?
See it?
Whoa, dude! That's
5!
So, there are
120
ways to arrange five books on a bookshelf.
(Aren't you glad I didn't make you draw them out?)
Was the answer to our
3-book
problem really 3!
?
Yep!
Will this always work?
TRY IT:
How many ways can
eight books be arranged on a bookshelf?
(reason it out with
slots)
Continued on the
next
page
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