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## Official Guide Explanation:Problem Solving #171

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: 171
Page: 176
Difficulty: 5 (Moderate)
Category 1: Algebra > Functions > Sequences
Category 2: Algebra > Exponents >

Explanation: With some sequences, it's a good idea to avoid figuring out every term and instead focus on the underlying principle. In this case, the numbers stay reasonably small, so it is probably easiest to figure out the terms themselves.

We're looking for the difference between the 5th and 6th terms:

s5 = 5 + 25 - 1 = 5 + 24 = 5 + 16 = 21

s6 = 6 + 26 - 1 = 6 + 25 = 6 + 32 = 38

The difference is 38 - 21 = 17, choice (E).

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