Composite Numbers
(KS2, Year 4)

The Lesson

A composite number is a number that can be divided exactly by at least one number that is not itself or 1. This means a composite number is any number (other that 1) that is not a prime number. For example,

• 4 is a composite number. It can be divided exactly by 1, 2 and 4. 4 is a composite number because it can be divided by 2 (which is not 1 or 4 itself).
• 5 is not a composite number. It can only be divided exactly by 1 and 5. 5 is a prime number because it can only be divided by 1 and 5 itself.

The Composite Numbers

The composite numbers are:In a number square, the composite numbers are shaded below:Note: This is the exact inverse of the prime numbers in a square. If this number square is overlaid with that of the prime numbers, all numbers (apart from 1) would shaded.

Composite Numbers Are Natural Numbers Greater Than 1

Composite numbers are natural numbers (the counting numbers: 1, 2, 3...) greater than 1.

Interactive Game on Composite Numbers

Here is an interactive game to help you learn about composite numbers.

• You are the fish.
• Pop the bubbles with composite numbers to collect red hearts. You need five to win.
• If a bubble with a composite number reaches the top, you will lose a red heart.
• Avoid the bubbles with prime numbers (i.e., non-composite numbers). If you pop one, you will lose one of your three lives.
• Good luck!
• The fish moves to wherever you taptowards your mouse clicks. (Hint: The farther the distance, the faster it moves.)

Factors

Numbers that divide exactly into another number are called factors. For example, the factors of 4 are 1, 2 and 4 because they all divide exactly into 4. Composite numbers must have more than 2 factors: 1, the composite number itself, and at least one other factor. This is in distinction to prime numbers which only have two factors: 1 and the prime number itself.