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## Official Guide Explanation:Data Sufficiency #143

Background

This is just one of hundreds of free explanations I've created to the quantitative questions in The Official Guide for GMAT Review (12th 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: 143
Page: 285
Difficulty: 5 (Moderate)
Category 1: Word Problems > Other >
Category 2: Arithmetic > Percents > Percent Change
Category 3: Arithmetic > Ratio and Proportion >

Explanation: To find out the current relationship between stocks Y and X, you need some other relationship between them, or the amount of stocks Y and X. Statement (1) gives you the relationship: if they were equal, you can determine the present relationship after each price was altered by a percentage.

Statement (2) is also sufficient. The increase in the price per share of X was 10% of x, or (0.1)x. The decrease in Y was (0.1)y. The statement gives an equation: (0.1)x = (10/11)(0.1)y. That equation can be manipulated to produce the ratio ((y)/(x)), from which you can answer the question. The mechanics of solving for the percent aren't important: it's recognizing that any relationship between the changes in Y and X is enough to establish their present ratio. Choice (D) is correct.

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