What is the probability of rolling a composite number with one roll of a die?

A composte number is any number that is not prime.

The numbers 1, 2, 3, 4, 5 and 6 appear on a die.

2, 3 and 5 are prime numbers; and one 1 is niether prime nor composite (unit).

Therefore, 4 and 6 are composite. So the probability or rolling a composite number is 1/3 (2/6).