Select a random number representing a row

How can i make this thing in PL/SQL?

I want to generate a random number, which will represent a position (row) from a list of results, which will be ordered by a field.

To give a more detailed thing, suppose we have

ID : 1,5,7,9,11,20,35

How can I generate a random number, that will be from these (1,5,7,9,11,20,35) ?