Permutation Calculator

Calculate the number of permutations P(n, r), which is the number of ways to choose r items from a set of n items where the order of selection matters.

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What is Permutation?

In mathematics, a permutation is an arrangement of objects in a specific order. The number of permutations of selecting r objects from a set of n distinct objects is given by the formula:

$$P(n, r) = \frac{n!}{(n-r)!}$$

Here, n! (n factorial) is the product of all positive integers up to n, and (n-r)! is the factorial of n-r.

Permutations are used in various fields such as combinatorics, statistics, and computer science to count the number of possible arrangements or sequences of objects when order is important. For example, determining the number of ways to arrange letters in a word or selecting a batting order for a baseball team involves permutations.

Example

Suppose you want to find out how many ways you can arrange 2 letters from the set {A, B, C}. Here, n=3 and r=2. Using the formula:

$$P(3, 2) = \frac{3!}{(3-2)!} = \frac{3!}{1!} = 3 \times 2 \times 1 = 6$$

The possible permutations are: AB, AC, BA, BC, CA, CB, which are indeed 6 permutations.