When you roll a six-sided number cube you can get the following possible results:
Then, you have 6 possible result.
To find the probability of rolling P(odd or 2) you find the set of numbers in the possible results that are odd or 2:
You have 4 possible results that are odd or 2.
Then, the probability is: The possible results that are odd or two divided in the total of possible results
Then, the probability of rolling odd or 2 is 1/3