if you have the letters A,B,C,D,E and you form 3 letter "words" with these letters, what is the probability that the wordstarts with D?

how do I show this using permutations?

using fractions I know the answer is $\displaystyle \frac{1}{5}$ (1/5 *4/4*3/3)

so it would be $\displaystyle \frac{something}{_{5}P_{3}}$

how do I show the number of possible combinations that begin with D as a permutation?