Arithmetic (Beginner) · Quick Reference

Numbers Cheat Sheet

Arithmetic (Beginner) · Lesson 1/21

In one line: numbers are the building blocks of mathematics. Before we can add, subtract, or solve problems, we need to understand what numbers are and the different families they belong to.

Key Ideas

1Natural Numbers. Counting numbers starting from 1: 1, 2, 3, 4, 5, ... (do not include 0 or negatives).

2Whole Numbers. Natural numbers plus zero: 0, 1, 2, 3, 4, ...

3Integers. Whole numbers plus their negatives: ..., -3, -2, -1, 0, 1, 2, 3, ...

4Rational Numbers. Any number that can be written as a fraction a/b, where b is not 0. Examples: 1/2, -3/4, 5 (since 5 = 5/1).

5Even and Odd Numbers. Even numbers are exactly divisible by 2 (2, 4, 6...). Odd numbers are not (1, 3, 5...).

Worked Examples

Classify -7, 0, 4, and 2/3 as natural, whole, integer, or rational.

-7: integer, rational | 0: whole, rational | 4: natural, whole, integer, rational | 2/3: rational

Is 17 a prime number?

Yes, 17 is prime.

List all even numbers between 10 and 20.

12, 14, 16, 18

Practice Yourself

Is -5 a whole number?

No — whole numbers cannot be negative.

Give an example of a composite number between 1 and 10.

4, 6, 8, or 9

Is 0 a natural number?

No, but it is a whole number.

Write 3 as a fraction to show it is rational.

3/1