Rolling a 1 or a 2 are mutually exclusive events (if you roll a 1, you could not have rolled a 2, and vice-versa), so the probability here is additive:
P(1 or 2) = P(1) + P(2) = 1/34 + 1/34 = 2/34 = 1/17.
So the probability of rolling a 1 or a 2 is 1/17.
