easy way to remember which formula to use among: aCn, aPn, and n!

Hi..
Arrangements too mean that the order the items are placed is important..
It is same as choosing but with order important.

Now difference in ordered and unordered.
Unordered..
1) choose a team of 11 from 16.
2) way to eat 5 different sweets out of 7 that are available.
Here who you choose first or what you eat first does NOT matter.

Ordered...
1) ways to seat 11 person out of 16.
2) ways to place 5 sweets in 5 different shaped boxes.
Here who sits on which chair is important.

Hi chetan2u,

I think that solves my query, thank you so much.

So do you think this is the right thought flow to identify which formula to use (sorry if I am bothering with too many questions, but my exam is 11 days away, and so far P&C is my biggest weakness )

1. identify whether it is an 'arrangement' question or 'select question'

2. if it is an 'arrangement' question, we have to use the Permutation formula, or the n! formula (divide by a! where a=similar elements)

3. if it is a 'choose' / 'select' question then first identify whether it matters how we choose. If order matters, i.e. abc is not the same as cab then select use combination formula. If order doesn't matter then use the permutation formula

Is there anything I am missing?