Read the following SAT test question and then click on a button to select your answer.

　　The population of Norson, the largest city in Transitania, is 50 percent of the rest of the population of Transitania. The population of Norson is what percent of the entire population of Transitania?

　　(A) 20%

　　(B) 25%

　　(C) 30%

　　(D) 33 and (1/3)%

　　(E) 50%

　　Explanation

　　Let N equal the population of Norson, and let T equal the entire population of Transitania. Then T-N is the population of the rest of Transitania.

　　N is 50% of (T-N).

　　N = (1/2)*(T-N), or 2*N = T-N.

　　This gives 3*N = T, or N = (1/3)*T.

　　So the population of Norson is one third, or 33 and (1/3)%, of the entire population of Transitania.

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（编辑：马菲）