Permutation & Combinations Flashcards by Hector .

Q

nPn =

A

n!

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Q

nPr =

A

n!/(n-r)!
= nCr x r!

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Q

nCr =

A

n!/(n-r)!r!

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Q

If r>n/2, nCr

A

nC(n-r)

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Q

nC(r-1) + nCr =

A

(n+1)Cr

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Q

(a+b)^n =

A

nC0 a^n + nC1 a^(n-1)b + nC2 a^(n-2)b^2 + …

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Q

nCr . a^(n-r).b^r =

A

n!/(n-r)!r! a^(n-r).b^r

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