Number Theory

Lesson

We can make any number by using its factor pairs. Every number will have at least one factor pair, $1$1 and itself.

When we're completing factor expressions we need to think of a second number we can use to complete an expression. We can do this by counting or maybe dividing. Let's look at an example...

Complete the factor expression below

$\editable{}$$\times$×$7=21$7=21

Here we need to complete the factor expression by finding what goes in the $\editable{}$.

So far we know two numbers $7$7 and $21$21. We can use these two numbers to work out the missing number.

We can either find the result of $21\div7$21÷7 or we can count by $7$7's.

If we count by $7$7's we get...

$7$7, $14$14, $21$21.

On a number line it would look like this...

We can now see that we'll have to count by $7$7 three times before we get to $21$21, so $3$3 groups of $7$7 make $21$21.

So, the number $3$3 completes the factor expression.

$3\times7=21$3×7=21

Remember!

We can use the multiplication tables to help us work out factors of a number.

Use the sliders below to find that factor pair.

Fill in the box with the missing number.

$6\times\editable{}=60$6×=60

Fill in the box with the missing number.

$11\times\editable{}=22$11×=22

Fill in the gaps to find all factor pairs of $66$66.

$1,\editable{}$1,

$2,\editable{}$2,

$3,\editable{}$3,

$11,\editable{}$11,