confused where to apply permutation & where combination.

Analyize the question. Read the question clearly and see what is given in the problem and what is needed to solve.

See the problem is of permutation or combination.

The basic rule is that if the order of selection matters, then it is a permutation and if the order of selection does not matter, then it is a combination

for example This is permutation problem

 An organization surveys viewers  and asks for their favorite and least favorite shows from a list of 10shows. How many possible responses are there?

There are 10! responses