How many different 2-letter combinations exist in this list of 2-letter permutations? AB, BA, AC, CA, BC, CB

Hey there! I'm happy to help!

A permutation is focused on a specific order, while a combination is not focused on the order but on the content of what is grouped.

AB and BA are different permutations because they are in different orders, but they are the same combination because they both contain the letters A and B.

So, we see that AB and BA are one combination.

AC and CA are also another combination because they are made up of the letters A and C.

Same goes for BC and CB, this is also one combinations.

This totals up to C. 3 combinations. Now you know the difference between permutations and combinations!

Have a wonderful day!

341

step-by-step explanation:

all you have to do is 9x31 (which equals 279) and then 20x31 (which equals 620). then you have to subtract. 620-279=341.