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Official Guide Explanation:Problem Solving #15

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: 15
Page: 63
Difficulty: 4 (Moderately Easy)
Category 1: Geometry > Quadrilaterals >
Category 2: Word Problems > Geometry Problems >
Category 3: Arithmetic > Percents > other

Explanation: If the rug is 9 by 12, the area of the rug is 9(12). If 60\of the floor is covered by that rug, ((6/10))f = 9(12). To solve: f = (9)(12)((10/6)) = (9)(2)(10) = 180, choice (C). Note that you never needed to find the area of the rug--in fact, it was easier to do the problem without taking that intermediate step. Often, right after doing multiplication, you'll find yourself doing division with the same number. It takes some practice to know when to avoid multiplying, but try it out--worst case scenario, you'll just have to multiply later on.

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