Problem
COM-B1-M01-P008 No Equal Adjacent Letters
#8
★★☆☆☆ Level 2 of 5
How many words of length \(4\) over \(\{A,B,C\}\) have no two adjacent equal letters?
Choose the first letter freely; each next letter must differ from the previous one.
First letter: \(3\) choices. Each of the next three letters: \(2\) choices. Total: \(3\cdot2^3=24\).
Typical dependent choice.