Fundamental counting principle: If the first event could occur in m ways and the second event could occur in n ways, then the number of ways that the two events could occur in sequence is \(m \cdot n\).
We only use the first 3 letters from the alphabet: a, b, c
First letter: 3 ways Second letter: 2 ways (as no letter is used more than once)
By the fundamental counting principle: \(3 \cdot 2=6\)
Thus there are 6 2-letter code words that can be formed from the first three letters in the alphabet such that no letter is used more than once.