Solution
No Letter Twice in a Row
Show the problem again
How many 8-letter words can be formed from the alphabet {A, B, C} if no two adjacent letters are equal? (Any string counts as a word.) Give an integer.
Worked solution
The answer is 384. The first letter can be any of 3. Each later letter can be anything except the letter immediately before it, so it has exactly 2 choices regardless of history. The total is 3 × 2⁷ = 384.
Source: Classic counting exercise in wide circulation; no traceable original source. Statement written for AxiomIQ.