When asked to find the number of different ways to arrange items, create a systematic list. Start by fixing the position of one item and listing all arrangements for the remaining items, then repeat for each starting item.
Example 1: To arrange the letters A, B, C, first fix A: A-B-C, A-C-B. Next, fix B: B-A-C, B-C-A. Finally, fix C: C-A-B, C-B-A. This gives 6 total arrangements.
Example 2: Three friends, Tom, Sam, and Liz, are in a line. The possible orders are: Tom-Sam-Liz, Tom-Liz-Sam, Sam-Tom-Liz, Sam-Liz-Tom, Liz-Tom-Sam, Liz-Sam-Tom. There are 6 ways.
To find every possible way to arrange a group of items in a line, you need a system so you do not get lost or repeat yourself. The trick is to be methodical: place one item in the first spot and list all the ways the others can be arranged. Then, pick a new item for the first spot and do it again.