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Official Guide Explanation:Data Sufficiency #111

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: 111
Page: 161
Difficulty: 5 (Moderate)
Category 1: Algebra > Functions > Sequences

Explanation: Given the rule for this sequence, if we know the first two terms, we can determine all of the successive terms. The same principle applies later in the sequence: If we know two consecutive terms, we can figure out all the later terms.

Statement (1) is sufficient. Since the 6th term is the sum of the 4th and 5th, if the 6th minus the 4th is 5, then the 5th term is 5. That's all we know, but that's what the question is asking for!

Statement (2) is insufficient. The sum of the 6th and 7th terms is the 8th term, so we know the value of the 8th term, but we don't know anything else. Choice (A) is correct.

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