Answer:
Whenever the position matters, use permutation.
If position does not matter, then it's a case of combination.
Explanation:
Consider the provided information.
Whenever the position matters, use permutation.
For example: If (X,Y) and (Y,X) are different, it is a permutation question.
In Permutations every small detail matters.
For example: David, John and Stuart is different from John, David, and Stuart (As the order is different).
If position does not matter, then it's a case of combination.
For example: (X,Y) is the same as (Y,X), It is a combination question.
In Combinations the small details don’t matter.
For example: David, John and Stuart is not different from John, David, and Stuart.