Official Guide Explanation:
Data Sufficiency #55

Background

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Solution and Metadata

Question: 55
Page: 277
Difficulty: 5 (Moderate)
Category 1: Word Problems > Other >
Category 2: Arithmetic > Percents > other

Explanation: The question gives us a formula:

n = g - d

We want to know how much n changes (in percentage terms) when g and d increase.

Statement (1) is insufficient: it only tells us of a change in g.

Statement (2) is also insufficient, only mentioning d.

Taken together, the statements are still insufficient. The result of the two changes is 1.04g - 1.15d. We don't know how that compares, in percentage terms, to g - d, because we don't know how the values of g and d themselves compare. If g and d are the same, we'd know how the 4 percent and 15 percent relate, but the relationship changes if g and d differ. Choice (E) is correct.

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