Assume all strings of three lowerca

Assume all strings of three lowercase letters are equally
probable. Then what’s the probability of a string of three
vowels?
There are 26 letters, of which 5 are vowels. So there are
N
=
26
3
three letter strings, and
n
=
5
3
consisting only of
vowels. Each outcome (string) is equally likely, with probability
1
N
, so event
A
(a string of three vowels) has probability
p
(
A
) =
n
N
=
5
3
26
3

0
:
00711.