Every competition participant should learn modular arithmetic, or MOD in short. This is because a majority of number theory problems are MOD related. This tutorial covers MOD basics. A separate course will cover more advanced topics.

Prerequisite:

Students should be familiar with the regular arithmetic operations (addition, subtraction, multiplication, division, and exponentiation) and

Contents

• MOD definition
• Basic operations and properties
• Evaluate MOD expressions and related techniques (e.g. negative one technique etc)
• Solve sum of digits problems (The MOD by 9 technique)
• Solve ending digits problem

• For more complete and detailed description of MOD, please refer to the book  Number Theory (MOD) .
• Supplementary reading