I'm basically saying the same thing you are. Answering the question by picking one of the 4 answers cannot be done, both 50% and 25% contradict each other. You're wrong as soon as you pick an answer.
My friend posted this on his fb so i thought I'd see your responses since the airplane on a conveyor belt was so entertaining.
If you choose an answer to this question at random,
If the answer is (b) or (c) it's 25%. If the answer's (a) or (d) it's 50%. So the answer is dependent on the probability of the answer, being 1/3.
So:
1/3 x 2/4 = 2/12
1/3 x 1/4 = 1/12
1/3 x 1/4 = 1/12
= 1/3 or 1 in 3
The question does not appear to be stated. What question are you answering?
I assumed the question was irrelevant.