Count the possible combinations of 3 letters chosen from A, B, C, D. The possible combinations of 3 letters are __.

Step-by-step explanation:

We are given the letters:

2

We write the possible permutations of 3 letters from the given list:

3

Because order is not important in a combination we cross out the duplicate pairs:

4

4

Step-by-step explanation:

n! / r!(n-r)!

n = # of total objects

r = # grouped together at a time

4! / 3!(4-3)!

4