How many strings of length 12 can we compose using letters A,B,C, and D if every letter should appear at least once?
can someone walk me through this? I believe using the concept of the sieve formula is what i am supposed to use but I can't figure out where to start, my first thought is that 12! is the total number of permutations but then I know i have to take into account that each letter must be used once but I can't get any farther
EDIT: total number of strings with no restrictions is 4^12
please if someone can walk me through that would be great