A permutation is a mathematical technique that determines the number of possible arrangements in a set when the order of the arrangements matters.

The permutation feature importance is defined to be the decrease in a model score when a single feature value is randomly shuffled 1.

**Formula to calculate permutations.**

n is the total number of objects.

r is the number of objects selected.

**Example:**

Suppose you took 2 cakes from a packet of 6 cakes. Calculate the permutations.

Therefore, the permutations are 30.