The odd probability of A is 1/2, and the even probability of B is 1/2, so the first question is (C2,1) x1/2 =1/2.
Second, at least one of A and B is odd. We can say from the opposite side that there is a probability that A and B are not odd numbers, that's all.
1/2x1/3 =1/6, then the probability that at least one of Party A and Party B is odd is 1- 1/6 = 5/6.
Finally, the number of performance units of Party A and Party B can be 0, 1, 2, 3 and 4, and their probabilities are as follows.
0 1 2 3 4