3 letters only in duck language
Source: (2021-) 2022 XV Dürer Math Competition Finals Day2 E1
December 1, 2022
combinatorics
Problem Statement
In duck language, only letters , , and are used. There is no word with two consonants after each other, because the ducks cannot pronounce them. However, all other four-letter words are meaningful in duck language. How many such words are there?
In duck language, too, the letter is a vowel, while and are consonants.