Permutation Calculator — Formula
## How to Calculate Permutations
### Formula
**P(n, r) = n! / (n - r)!**
A permutation counts the number of ways to arrange r items chosen from n distinct items where order matters. For example, selecting a president, vice-president, and secretary from 10 people is a permutation problem because each position is different.
### Formula
**P(n, r) = n! / (n - r)!**
A permutation counts the number of ways to arrange r items chosen from n distinct items where order matters. For example, selecting a president, vice-president, and secretary from 10 people is a permutation problem because each position is different.
Esempio Risolto
How many ways can you arrange 3 books from a shelf of 10?
- P(10, 3) = 10! / (10 - 3)!
- = 10! / 7!
- = 10 * 9 * 8 = 720
- Compare with combinations: C(10,3) = 120 (order does not matter)