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Permutations

★★☆☆☆Middle School

📖Definition

A permutation is the number of ways to arrange r items from n items where order matters.

P(n, r) = (n!)/((n-r)!)

Permutation formula

n! = n × (n-1) × ·s × 2 × 1

Factorial

P(n, r) = n × (n-1) × ·s × (n-r+1)

Permutation expanded

예제 1

Find the number of ways 5 people can line up.

예제 2

Choose president, VP, secretary from 10 people.

Password possibilities

Task ordering

Ranking combinations

#순열#경우의수#permutations#counting