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## Official Guide Explanation:

Problem Solving #190

**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.

Click here for an example of the PDF booklets. Click here to purchase a PDF copy.

**Solution and Metadata**

**Question****: 190**

Page: 179

Difficulty: **5** (Moderate)

Category 1: Arithmetic > Properties of Integers > Other

**Explanation:** When looking for the units digit of very big numbers like this one, realize that you don't have to worry about the rest of the number. For instance, to find the units digit of 13 * 13, just multiply the units digits: 3 * 3 = 9. So, the units digit of 13^{4} is the units digit 3 * 3 * 3 * 3 = 81, or 1. The units digit of 17^{2} is the units digit of 7 * 7 = 49, or 9. \newline The units digit of 29^{3} is the units digit of 9 * 9 * 9 = 729, or 9. So, the units digit of the whole thing is the units digit of 1 * 9 * 9 = 81, or 1, choice (E).

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