The first book you select can be any one of 700.
. . . For each of those ...
The second book can be any one of the other 699.
. . . For each of those ...
The third book can be any one of the remining 698.
The total number of ways to gather three books from the shelves into your hands is (700 · 699 · 698) = <em>341,531,400 ways</em> .
<em>BUT ...</em>
When you bring three books to the check-out counter, Marian the Librarian doesn't know in which order you took them down off the shelves. You could have gathered the same three books in (3 · 2 · 1) = 6 different ways.
So, even though there are 341,531,400 ways to<em> </em>gather up three books, there are only (341,531,400 / 6) = 56,921,900 different GROUPS of three books that you can choose to take home.
