Probability that the sum of two elements in a set is divisible by 3. Select 2 integers from the set $\{1,2,3,4,5,6,7,8\}$. What is the probability that their sum is divisible by 3? I am assuming this is without replacement although this is not explicitly stated. 
My answer: There are $\binom{8}{2}$ ways of selecting two elements. Only 6 of these pairs $(1,2), (4,5), (4,2), (7,8),(3,6), (2,7) $ are divisible by 3. Thus $P=6/\binom{8}{2}$. Is this correct?

The possible pairs are $(1,2), (1,5),(1,8),(2,4),(2,7),(3,6),(4,5),(4,8),(5,7)$and $(7,8)$ thus there are 10 possible pairs out of 28 pairs. So the probability of the sum is divisible by 3 is 0.357
