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Official Guide Explanation:Problem Solving #108

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: 108
Page: 167
Difficulty: 6 (Moderately Difficult)
Category 1: Arithmetic > Decimals >

Explanation: First, recognize that if you combine an equal number of 2's and 5's, you'll have a power of 10. In this case, we can rewrite the expression as:

(1/(262353))

= (1/(26103))

= (1/(26)) * 10-3

26 is 64, so (1/(26)) = (1/64). (1/64) is somewhere between 0.01 ((1/100)) and 0.02 ((1/50)). The exact number doesn't matter for this question, so let's call it 0.015. That gives us:

0.015 * 10-3

Move the decimal point three spaces to the left:

0.000015

There are four zeros between the decimal point and the first nonzero digit. (B) is correct.

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