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## Official Guide Explanation:

Data Sufficiency #D31

**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.

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**Solution and Metadata**

**Question****: D31**

Page: 24

Difficulty: **6** (Moderately Difficult)

Category 1: Arithmetic > Descriptive Statistics > Standard Deviation

**Explanation:** Statement (1) is sufficient. You will rarely see the term "variance" on the GMAT; when you do, recognize that it is the square of the standard deviation. It's that simple--if the variance for the set is 4, the standard deviation is rt[4] = 2.

Statement (2) is also sufficient. It is a long - winded definition of standard deviation. SD measures the average difference between the mean and each term in the set. If every term in the set is 2 away from the mean, the average distance is 2, meaning that the SD is 2. Choice (D) is correct.

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