This is the second part of the Introduction to Modular Systems Series. Please read the first part before proceeding. Last Monday, we have learned a number system that uses numbers on the 12-hour analog clock. We have performed addition using these numbers and discovered that in that system, 12 behaves like 0. We have also observed […]

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# Number Theory

## Introduction to Clock Arithmetic and Modular Systems

Most of us are familiar with 12-hour analog clocks. They are numbered 1 through 12; they have hour, minute, and second hands. In this post, we are going to experiment clock arithmetic — we are going to perform addition using the numbers on the clock. Let us think about the following questions. What if we […]

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## Divisibility by 5 and 10

This is the third post in the Divisibility Rules Series. The first was about divisibility by 2 and the second was about divisibility by 4. In this post, we discuss divisibility by 5 and 10. If we skip count by 10, we will immediately realize that the numbers always end in zero: 10, 20, 30, […]

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