The correct answer is D
Explanation
Let N equal the population of Norson, and let T equal the entire population of Transitania. Then T minus N is the population of the rest of Transitania.
N is 50% of (T minus N).
N = (1 over 2) times (T minus N), or 2 times N = T minus N.
This gives 3 times N = T, or N = (1 over 3) times T.
So the population of Norson is one third, or 33 and (1 over 3)%, of the entire population of Transitania.