I'm studying the chapter of counting for my discrete math exam and I'm getting a bit confused with the terms permutations/combinations, elements and ways.
As far as I know:
- Permutations/combinations are an arrangement of ordered/unordered distinct elements.
- Elements are what permutations/combinations are made of.
- When we refer to the number of permutations/combinations of an arrangement, we mean how many ways we can do a permutation/combination of that arrangement.
But then there are also the terms r-permutation and r-combination where $r$ are the elements of an arrangement. So, when we do a permutation $P(n,r)$, what is $n$ then? I thought $n$ was the number of elements of our set.
Here's one of the references I used:
I'm a little bit confused... Could someone clarify this for me?
Thank you in advance.