Hi, I am not sure which formula will allow me to get the following results. If I have to pick two letters from A, B, C, D, then there are 6 possible combinations: AB AC AD BC BD CD. Now assume that letter D has turned into another A, i.e. A2. Now my combinations have changed to A1B A1C A1A2 BC BA2 CA2 So I eliminate BA2, and CA2 and I have 4 unique combinations. I know that in the case of permutations with repetitions, we divide the nPr formula by the factorials of the frequency of the letters, but I am not sure how it is done with combinations. What formula can use for combinations? Thanks.