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## Official Guide Explanation:Problem Solving #139

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: 139
Page: 80
Difficulty: 5 (Moderate)
Category 1: Geometry > Rectangular Solids and Cylinders > Rectangular Solids
Category 2: Arithmetic > Ratio and Proportion >

Explanation: Say that the edge of cube Y is e. Then, if the edge of cube X is twice that of cube Y, the length of an edge of cube X is 2e. The volume a cube is s3, so the volume of cube Y is e3, and the volume of cube X is (2e)3. Then, the ratio of the volume of Y to the volume of X is e3:8e3, or 1:8, which can also be written as a fraction, (1/8), choice (D).

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