The word CARLETON have 8 letters. We want to arranged this word so that it contains either CA of AC as sub-words.
The letters C and A can be grouped and considered as a single letter. that is, (CA)RLETON.
Hence we can assume total letters as
Thus, the total number of arranged so that the word contains either CA or AC as sub-words are 10080.
Let A, B, and C be sets. Show that