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## Official Guide Explanation:Problem Solving #135

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: 135
Page: 171
Difficulty: 5 (Moderate)
Category 1: Arithmetic > Counting Methods > Permutations
Category 2: Word Problems > Geometry Problems >

Explanation: This is a complicated problem with a simple solution. There are three different places in which the mouse must make a decision. At the second point to the right of X, the mouse can take the higher or lower path, giving it two options. At the second decision point (the beginning of the middle quadrilateral), the mouse again has two options. At the third decision point (the left side of the quadrilateral with the line through it), the mouse can take any of three paths. From this point, it's a permutation problem. To find the total number of possible routes, multiply the number of options at each point: 2 * 2 * 3 = 12, choice (C).

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