How many 4-letter words with at least one consonant can be constructed from the letters A, B, C, D, E, and F? (Note that B, C, D, and F are consonants, any word is valid, not just English language words, and letters may be used more than once.)
You have 6 letters: A, B, C, D, E, F. Since they can be repeated, you will therefore have: 6^4 =1,296 permutations, or 4-letter "words". But each "word" must have at least one consonant. Therefore, we have to remove ALL 4-letter "words" that are only vowels. There are very few such permutations. Beginning with "A", there are only 8 such permutation as follows:
AAAA, AAAE, AAEA, AAEE, AEAA, AEAE, AEEA, AEEE.
Similarly, beginning with "E", there are also 8 such permutations.
So then, the total number of 4-letter permutations or "words" =6^4 =1,296 - 8 - 8 =1,280 such 4-letter "words"