**Missing Numbers** *KS2 Revision*

## What you need to know

**Things to remember:**

- It doesn’t matter what order you add or subtract numbers, so you can move them all around.

Find the missing number in the following equation:

5 + [?] - 2 = 7

Before we start, it is important to remember that the order we do additions and subtractions doesn’t matter.

2+9-3=8

9+2-3=8

-3+2+8=8

Now, back to our question

5 + [?] - 2 = 7

We will do this in 3 steps.

**Step 1:** Move what we are looking for to the start of the equation.

5 + [?] - 2 = 7

[?] + 5 - 2 = 7

**Step 2:** Do the addition or subtraction for the numbers next to each other

** **

[?] + 5 - 2 = 7

5-2 =3

[?] + 3 = 7

** **

**Step 3: **Find your missing number.

We can do this in two ways:

**Step 3a: **Try thinking about what the question is saying.

[?] + 3 = 7

This is telling us that “something plus 3 is 7”. But, we know that we add 3 to 4 to make 7, so 4 must be our answer!

**Step 3b:** Rearrange to get what we are looking for by itself.

*Hint: **Remember, we do the opposite to get something by itself.*

* *

[?] + 3 = 7

[?] = 7 - 3

[?] = 4

So, as we can see, it doesn’t matter if we use **3a** or **3b**, we get the same answer!

## Example Questions

**Question 1:** Find the missing number in the following equation:

12 + [?] + 9 = 33

**Step 1:** Move what we are looking for to the start of the equation.

12 + [?] + 9 = 33

[?] + 12 + 9 = 33

**Step 2:** Do the addition or subtraction for the numbers next to each other

** **

[?] + 12 + 9 = 33

12+9 =21

[?] + 21 = 33

** **

**Step 3: **Find your missing number.

We can do this in two ways:

**Step 3a: **Try thinking about what the question is saying.

[?] + 21 = 33

This is telling us that “something plus 21 is 12”. We can make 33 by adding 12 to 21, so 12 must be our missing number.

**Step 3b:** Rearrange to get what we are looking for by itself.

*Hint: **Remember, we do the opposite to get something by itself.*

* *

[?] + 21 = 33

[?] = 33 - 21

[?] = 12

**Question 2:** Find the missing number in the following equation:

11 + [?] -15 = 1

**Step 1:** Move what we are looking for to the start of the equation.

11 + [?] + -15 = 1

[?] + 11 - 15 = 1

**Step 2:** Do the addition or subtraction for the numbers next to each other

** **

[?] + 11 - 15 = 1

11-15 =-4

[?] -4 = 1

** **

**Step 3: **Find your missing number.

We can do this in two ways:

**Step 3a: **Try thinking about what the question is saying.

[?] + 21 = 33

This is telling us that “something subtract 4 is 11”. We can make 1 by subtracting 4 from 5, so 5 must be our missing number.

**Step 3b:** Rearrange to get what we are looking for by itself.

*Hint: **Remember, we do the opposite to get something by itself.*

* *

[?] -4 = 1

[?] = 1 + 4

[?] = 5