Official Guide Explanation:
Data Sufficiency #143

Background

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Solution and Metadata

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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