when there is a probability this OR that, the individual probabilities are added.
probability of rolling an even number is 1/2
prime numbers between 1-16 are {2, 3, 5, 7, 11, 13} of these five are odd.
probability of rolling an odd prime number
5/16
probability of even OR odd prime
1/2 + 5/16
8/16 + 5/16 = 13/16
13/16 = 0.825
