How do you calculate permutations using the formula?

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Answer 1 · 2014-11-04T19:22:05

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 $5 * 4 * 3 = 60$