Question

How many six-letter "words" can be formed from the letters A, B, C, D, E, F, if each letter can be used only once?

Answer 1

\(6P6 = 6!\)

Answer 2

Another explanation is:
You have six slots
_ _ _ _ _
You may fill six letters in the first, so six possibilities.
Since one letter got taken, then we have five..

it goes down till 1.

Answer 3

Now you multiply \(6 \times 5 \times 4 \times 3 \times 2 \times 1\).