$\"\"$

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The premutation is $\"\"$

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The permutation formula is $\"\"$ .

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$\"\"$ (Apply permutation formula)

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$\"\"$ (Subtract denominator: $\"\"$ ) $\"\"$

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$\"\"$ (Expand factorials)

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$\"\"$

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$\"\"$ (Cancel common terms) $\"\"$

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The number of permutations are 1.

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