Official Guide Explanation:
Data Sufficiency #63

Background

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Solution and Metadata

Question: 63
Page: 157
Difficulty: 6 (Moderately Difficult)
Category 1: Arithmetic > Sets > 2 sets
Category 2: Word Problems > Sets >
Category 3: Arithmetic > Percents > other

Explanation: From the information in the question, you know the number of people in Town T and can figure out the number of females in Town T. Statement (1) is insufficient: we don't know the number of female residents born in Town T or the number of male residents not born in Town T, so we can't use that equation to determine anything.     \qquad

Statement (2) is insufficient: the number of female residents born in Town T (b) plus the number of female residents not born in Town T (n) is the total number of female residents, 12,000, so b + n = 12,000. Also, the statement tells us that n = 2b, so we can find the number of female residents born and not born in Town T. However, that doesn't give us the total number of residents who were born in Town T. (4,000 were born in Town T; 8,000 were not.)

Taken together, the statements are sufficient. If 4,000 (the number of female residents who were born in Town T) is twice the number of male residents who were not born in Town T, the number of male residents who were not born in Town T is 2,000. Thus, the total number of residents who were not born in Town T is 2,000 + 8,000 = 10,000. Since there are a total of 20,000 residents, that leaves 10,000 who were born in Town T. The correct choice is (C).

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