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## Official Guide Explanation:Data Sufficiency #19

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: 19
Page: 274
Difficulty: 5 (Moderate)
Category 1: Algebra > Functions > Sequences

Explanation: To answer a question about a sequence, we not only need to know the rule the sequence follows, but also at least one term in the sequence.

Statement (1) is insufficient. We're given one term (the first) in the sequence, but no way to figure out how to get from the first term to the 192nd term.

Statement (2) is also insufficient. This statement gives us the rule, but without knowing at least one term in the sequence, we can't use that rule to get us the 192nd term.

Taken together, the statements are sufficient. If each term is 3 less than the previous one, we can start with the first term (-40) and generate the second term, then the third, up to the 192nd. Of course we won't do that during the test, but we can quickly recognize that we have the information necessary to do so. Choice (C) is correct.

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