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## Appendix A. Working with Numbers: Binary and Hexadecimal

You learned the fundamentals of arithmetic so long ago, it is hard to imagine what it would be like without that knowledge. When you look at the number 145, you instantly see “one hundred forty-five” without much reflection.

You generally see numbers in what is called the decimal format. There are, however, other formats that can be used for numbering. When working with computers, the two systems that come up the most are binary and hexadecimal. Understanding binary and hexadecimal requires that you reexamine the number 145 and see it not as a number, but as a code for a number.

Start small: Examine the relationship between the number three and “3.” The numeral “3” is a squiggle on a piece ...

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