# How do you calculate permutations using the formula?

Nov 4, 2014

Permutations are the way to take n things from r possibilities. There is no uniqueness required of the arrangements either.

The formula is {n!}/{(n - r)!} where n is the number of items and r is the number of arrangements.

The ! symbol is for factorials, which is denoted below:
n! = n * (n - 1) * (n - 2) * … * 2 * 1

So let us say we wanted 5 permutations of 3. We have:

{5!}/{(5 - 3)!

Which simplifies to

{5!}/{2!}

Which is

{5 * 4 * 3 * 2!}/{2!}

This becomes $5 \cdot 4 \cdot 3 = 60$