Set theory:
Let the college grads be group A and the experienced employees be group B.
A is 60% of the population, B is 36% of the population, and A U B (union of A and B) is 68%.
We want to know the size of A ∩ B (intersection of A and B -- that is the group of college grads with 10 yrs experience).
Now A U B = A + B - A ∩ B so A ∩ B = .6 + .36 - .68 = 0.28.
Therefore the probability is 28%.
This seems legit