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## Official Guide Explanation:Problem Solving #169

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: 169
Page: 176
Difficulty: 5 (Moderate)
Category 1: Word Problems > Rate Problems > other
Category 2: Arithmetic > Ratio and Proportion >

Explanation: This is a simple ratio question made more difficult with very large numbers. It's handy to know that 1 million = 1 * 106, and the question tells you that 1 billion = 1,000,000,000 = 1 * 109. Scientific notation will make this question a lot more straightforward. Set up the ratio like this:

(96/(100 * 106)) = ((x)/(3 * 109)). Convert 100 * 106 to 1 * 108, then cross - multiply:

96 * 3 * 109 = x * 108 Divide both sides by 108:

x = 96 * 3 * 10 = 288 * 10 = 2,880, choice (C).

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