How to easily remember permutations

Permutations with repetition are simple: n^r where N = number of items, R = items you choose

Without repetition is a little more complex because you are using factorials, here is the formula:

n = number of items, and R = items you choose again.

So, say you have 10 people, and you want to choose 3 to go on a trip with. What is N and what is R?

N will be the 10 people.
R will be the 3.

So your equation will look like 10! / (10 - 3) !

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