2021 April MIMC 10 Problems/Problem 4
Stiskwey wrote all the possible permutations of the letters (
is different from
). How many such permutations are there?
Solution
Use the theorem of over-counting (When arrange distinguishable items and
indistinguishable items, the total number of ways to arrange them is
.) Therefore, the number of permutations of AABBCCCD is
.