If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Lesson 3: Irrational numbers

# Classifying numbers review

Review whole numbers, integers, rational, and irrational numbers.  Then, practice identifying each.

## Whole numbers

$\text{Whole numbers}$ are numbers that do not need to be represented with a fraction or decimal. Also, whole numbers cannot be negative. In other words, whole numbers are the counting numbers and zero.
Examples of whole numbers:
$4,952,0,73$

## Integers

$\text{Integers}$ are whole numbers and their opposites. Therefore, integers can be negative.
Examples of integers:
$12,0,-9,-810$

## Rational numbers

$\text{Rational numbers}$ are numbers that can be expressed as a fraction of two integers.
Examples of rational numbers:
$44,0.\stackrel{―}{12},-\frac{18}{5},\sqrt{36}$

## Irrational numbers

$\text{Irrational numbers}$ are numbers that cannot be expressed as a fraction of two integers.
Examples of irrational numbers:
$-4\pi ,\sqrt{3}$

## How are the types of number related?

The following diagram shows that all whole numbers are integers, and all integers are rational numbers. Numbers that are not rational are called irrational.
What type of number is $\sqrt{5}$?