Question

# How many 2-letter code words can be formed from the first 3 letters of the alphabet if no letter can be used more than once?

Equation, expression, and inequalitie
How many 2-letter code words can be formed from the first 3 letters of the alphabet if no letter can be used more than once?

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 $$m \cdot n$$.
By the fundamental counting principle: $$3 \cdot 2=6$$