Official Guide Explanation:
Data Sufficiency #39




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Solution and Metadata

Question: 39
Page: 276
Difficulty: 4 (Moderately Easy)
Category 1: Algebra > Linear Equations-One Unk >
Category 2: Arithmetic > Ratio and Proportion >

Explanation: Statement (1), combined with the knowledge that the sample is 80 adults, gives us two equations. If we call the number of adults who are college graduates c and the number who are not n:

c + n = 80

n = 3c

That's two linear equations and two variables. That's always enough to find the variables, so it's sufficient.

Statement (2) is also sufficient. Again, we know:

c + n = 80

This time, we have the difference between the two variables as well:

n = c + 40

Once again, that's two linear equations and two variables. No need to solve, since we know we could solve. Choice (D) is correct.

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