Can we attempt this like:
1st space will be taken by any of the 12 books
2nd space will be taken by any of the 11 books
Thus, 12x11x10x9x8. This is a permutation formula, though!
I took the gmat the other day and one of the few problems that I can remember was a combo problem. Probably the reason I can remember it is because I thought i had these simpler combo problems in the bag and of course drew a blank.
Problem goes something like this.
There are 12 books that can be placed in only 5 spaces on a book shelf. How many different combinations of books can there be, order doesn't matter.
Is it 12C5?