Question

How do you determine when a counting problem involves a permutation or a combination?

Answer 1

The difference between combinations and permutations is ordering. With permutations we care about the order of the elements, whereas with combinations we don't. For example, say your locker “combo” is 5432. If you enter 4325 into your locker it won't open because it is a different ordering (aka permutation).
(On google)