Theory of Positive Integers

An exploration of the properties, relationships, and applications of positive integers in various mathematical contexts.

Basic Concepts

Divisibility and Multiples

Understanding Divisibility

Divisibility means one number can be divided by another without a remainder. For example, 12 is divisible by 3 because \( 12 \div 3 = 4 \), with nothing left over!

What Are Multiples?

A multiple of a number is what you get when you multiply that number by a positive integer. For example, multiples of 5 are 5, 10, 15, 20, etc.

Useful Tricks

  • A number is divisible by 2 if it ends in 0, 2, 4, 6, or 8.
  • A number is divisible by 5 if it ends in 0 or 5.

Where Do We See This?

Divisibility and multiples help us with time (minutes in an hour), organizing teams, and finding even groups.

Examples

  • 24 is divisible by 6 because \( 24 \div 6 = 4 \).

  • Multiples of 7: 7, 14, 21, 28.

In a Nutshell

Divisibility and multiples show how numbers fit together and help in grouping and sharing.