Problem: A person has one white, two red, and three green flags. How many different signals can they make, each containing four flags arranged one above the other?
My attempt:
We have 4 slots and 6 things to choose from. But among the 6 things, there are repetitions. I know how to account for repetitions when there are same number of things to choose from as the number of slots: no. of permutations is $$ = \frac{n!}{p! \times q! \times r!}$$ [given that there are p number of repetitions of first kind, q number of repetitions for second kind, and r number of repetitions for third kind]. How can I account for repetitions in this case?