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Official Guide Explanation:Data Sufficiency #124

Background

This is just one of hundreds of free explanations I've created to the quantitative questions in The Official Guide for GMAT Quantitative Review (2nd ed.). Click the links on the question number, difficulty level, and categories to find explanations for other problems.

These are the same explanations that are featured in my "Guides to the Official Guide" PDF booklets. However, because of the limitations of HTML and cross-browser compatibility, some mathematical concepts, such as fractions and roots, do not display as clearly online.

Question: 124
Page: 162
Difficulty: 6 (Moderately Difficult)
Category 1: Arithmetic > Fractions >
Category 2: Algebra > Equations >

Explanation: Another way to write the equation is:

((s)/(rs)) + ((r)/(rs)) = 4?

((r + s)/(rs)) = 4?

r + s = 4rs?

Statement (1) is sufficient: it's exactly the same as the last version of the equation, so it directly answers the question. Statment (2) is insufficient: it allows you to rewrite the initial equation as (1/(r)) + (1/(r)) = 4?, or (2/(r)) = 4?, or r = (1/2)?, but it doesn't answer the question of whether r = (1/2). Choice (A) is correct.

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