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Permutations and Combinations

How do you know when to use the permutation formula and the combination formula and which parts of the question to put as r and n?
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mqb2766
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Original post by nutshell00
How do you know when to use the permutation formula and the combination formula and which parts of the question to put as r and n?


Probably be useful to have a context about the sort of questions you're talking about?
If it's about choosing things, with replacement is usually permutations and without replacement is usually combination.
However, rather than blindly remembering the formulae, the problems are often simple enough (or can be simplified) to work out the formulae if you understand the ideas.

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