# How many possible orderings are there of the letters: N, N, B, B?

##### 1 Answer

6

#### Explanation:

When we're talking about doing orderings of letters, we're referring to a permutation, the general formula of which is:

Now if these 4 letters were all different, say

But in our case we have 2 sets of 2 two letters that are identical. To get rid of the number of permutations that are the same (for instance,

With 6 permutations, we should be able to list them all:

NNBB

NBNB

NBBN

BBNN

BNBN

BNNB