If memory serves (mind you I took this from my notebook when I was in GS... 11 years ago):
Now there are also some special cases like:
- If n is a number of objects and one of the objects is repeated x times, then without repetition (in arrangements) the number of arrangements would be n!/x!
- If n is a number of objects and one of the objects is repeated x times while another is repeated y times, then without repetition (in arrangements) the number of arrangements would be n!/(x!y!)
- If n is a number of placements, and there are three types of objects that are respectively repeated x, y and z times, then without repetition (in arrangements) and
having the repeated objects successively placed next to each other, the number of arrangements would be n!x!y!z!
[Edit] Arrangements is same as selections[/Edit]
Hope this helps.