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## Official Guide Explanation:Problem Solving #70

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: 70
Page: 70
Difficulty: 5 (Moderate)
Category 1: Arithmetic > Properties of Integers > Evens and Odds
Category 2: Arithmetic > Descriptive Statistics > Average

Explanation: Given that the least integer in S is 7 more than the least integer in T, we can pick some values to get a better grasp of what's going on. If we say the least in S is 1, then S is {1, 3, 5, 7, 9, 11,13, 15, 17, 19}. That means the least in T is -6, so T is {-6, -4, -2, 0, 2}. The average of either one is the midpoint of the least and greatest integers, so in S, it's 10; in T, it's -2. The difference is 12, choice (D).

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