Discrete Math (MACM 101 Question)

I need to understand this notation:

permutation general formula : nPr = n! / (n - r)! n stands for the total number of things we have, but what about r ?

\(r\) is the number of objects from the total \(n\) objects that you want to permute.

For example, if I have the set of characters \(\{a,b,c,d\}\), I can choose to permute any of up to 4 of the characters. Suppose I take just 2 of them. Then the formula predicts I should find \({}_4P_2=\dfrac{4!}{(4-2)!}=\dfrac{24}2=12\) possible permutations. Indeed, these are

\(\begin{matrix}ab&ac&ad\\ba&bc&bd\\ca&cb&cd\\da&db&dc\end{matrix}\)

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Discrete Math (MACM 101 Question)I need to understand this notation:permutation general formula : nPr = n! / (n - r)! n stands for the total number of things we have, but what about r ?

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Discrete Math (MACM 101 Question)

I need to understand this notation:

permutation general formula : nPr = n! / (n - r)! n stands for the total number of things we have, but what about r ?