Number Basics

Even or Odd Numbers

A whole number can either be odd or even.

An even number is a whole number that can be divided by $2$. For example $8$ is an even number as $8 div 2 = 4$ which is a whole number.

An odd number is a whole number that can’t be divided by $2$. For example $5$ is an odd number as $5 div 2 = 2.5$ which is not a whole number.

Positive and Negative Numbers

Numbers can also be either positive, if they are greater than $0$ or negative, if they are less than $0$.

A number line can be used to help visualise the difference between positive and negative numbers.

On the left of the number line you can see the negative numbers and on the right you can see the positive numbers. Number lines can be used to show how big a number is in comparison to another number.

On the number line above $4$ is the biggest number and $-4$ is the smallest number.

Factors and Multiples

A factor of a number is a whole number that divides into that number.

A question may ask your child to find common factors of two numbers. This can be done by listing the factors of both numbers and identifying numbers that appear in both lists.

A multiple of a number is found by multiplying a whole number by another whole number. The exam may ask your child to find common multiples of $2$ whole numbers. In a similar way to finding common factors, common multiples can be found by listing multiples of each number and identifying numbers that appear on both lists.

Prime Numbers

Prime numbers have exactly two factors, $1$ and themselves.

For example $11$ is a prime number as the only whole numbers that divide into it are $1$ and $11$.

• $1$ is not a prime number as it only has one factor.
• The smallest prime number and only even prime number is $2$.
• The ten smallest prime numbers are: $2,,3,,5,,7,,11,,13,,17,,19,,23$ and $29$.

Square and Cube Numbers

If you multiply a whole number by itself then you get a square number. There are a few different ways that square numbers can be written.

For example $5$ squared or $5 times 5 =25$, so $25$ is a square number.

Some handy notation that you might see uses indices to write square numbers e.g. $5 times 5 = 5^{2}$, as shown this is still equal to $25$.

Cube numbers are similar to square numbers except a whole number is multiplied by itself twice.

For example $3$ cubed would be $3 times 3 times 3 = 27$ so $27$ is a cube number. Similar notation can be used to express cube numbers e.g. $3 times 3 times 3 = 3^{3}$

Roman Numerals