Alex has four books of different sizes which he wishes to place on a bookshelf. Unfortunately, the bookshelf has a conspicuous hole at one end through which only the smallest book can fall. If he wishes for all his books to stay stationary, in how many ways can he arrange his books?
18, you have 3 choices for the bottom because you can't use the small one, 3 choices for the next because you can now use the small one, 2 for the next and finally 1. You multiply all of them to get 18
