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July 29th, 2018, 12:06 PM   #1
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Permutation formula

How to derive the permutation formula $\displaystyle P=n!$
Find permutation of elements $\displaystyle \{ x_1 , x_2 , ... , x_n \}$
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July 29th, 2018, 12:20 PM   #2
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pick a first element, there are n ways of selecting

pick a second element, there are (n-1) ways of selecting

repeat until 1 element left.

The product of the number of selections at each choosing is

$n \cdot (n-1) \cdot (n-2) \dots \cdot 2 \cdot 1 = n!$
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