Official Guide Explanation:
Data Sufficiency #33




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Solution and Metadata

Question: 33
Page: 155
Difficulty: 4 (Moderately Easy)
Category 1: Algebra > Linear Equations-Two Unk >
Category 2: Arithmetic > Percents > other

Explanation: The question gives us an equation: n + m + b = 720. To find n, we'll need a lot more information.

Statement (1) is insufficient. It gives us another equation: m = 0.8b. So far, we have two equations but three variables. There's no way to combine them to isolate n, so we'll have to wait for more information.

Statement (2) is sufficient. The equation here is: n = 0.6(m + b). Note what happens. While the question separates magainzes and books, (m + b) appears in this equation and the equation in the question stem. If we reduce the question to "newspapers" and "non - newspapers," (call those z) here are the equations:

n + z = 720

n = 0.6z

Two equations, two variables. That's enough information, and choice (B) is correct.

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