If a number is chosen at random from the following list, what is the probability that it is not prime? 2, 3, 5, 7, 11, 13, 17, 19

The list numbers  given is: 2,3,5,7,11,13, 17 and
19.

The number of numbers are
8.

Each of these numbers are
prime.

So the number of choices to make in a random choice
= 8.

Since all  the 8 numbers given in this list ,
 2,3,5,7,11,13 , 17 and 19,  are primes, we are sure that any number chosen is a prime
number.

Therefore number of favourable choices =
8.

The number possible choices is
8.

Therefore the probability that a chosen number from the
list at random (or otherwise) is a prime = 8/8 = 1.