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## Official Guide Explanation:Data Sufficiency #21

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: 21
Page: 154
Difficulty: 6 (Moderately Difficult)
Category 1: Word Problems > Other >
Category 2: Arithmetic > Properties of Integers > Other

Explanation: Statement (1) is sufficient. First, figure out the sum of the units digits on the original 36 cards. Each set of 9 has a sum of 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 = 45, meaning that the four sets of 9 have a total of 45(4) = 180, which is a units digit of 0. If the units digit of the sum of the remaining 35 cards is 6, that means that the missing card is a 4.

Statement (2) is also sufficient. It tells us the same thing that (1) did, only with some extraneous detail. Again, we can determine that the missing card is a 4. Choice (D) is correct.

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