# Complete the Sum to Find the Missing Number

In this worksheet, students will complete a calculation by adding in the missing number so that both sides are equal. It will strengthen their number skills.

Key stage:  KS 2

Curriculum topic:   Verbal Reasoning

Curriculum subtopic:   Complete the Calculation

Difficulty level:

### QUESTION 1 of 10

Calling all number detectives!

Look at this symbol:

We know it is the equals sign but what does it actually mean?

It means the same as and doesn’t just mean the answer.

Look at the following calculation:

43 - 7 = 12 x __

Both sides of the calculation are equal. The answer to 43 - 7 must be the same as the answer to 12 multiplied by something (our mystery number).

We need to work out the answer to the calculation on the left to help us work out the missing number on the right.

So 43 - 7 = 36.

We need to make the calculation on the right equal 36. 12 x 3 is 36. Therefore the missing number is 3.

Let’s try another to check we understand what is happening:

3 x __ = 5 + 7

Here we must work out the right side of the calculation to help us work out the missing number on the left.

So, 5 + 7 = 12.

3 x ? = 12

The missing number is 4 as 3 x 4 = 12.

3 x 4 = 5 + 7

Remember that equals means the same as and the answers on either side of the equals sign must be the same.

In this activity, you will be completing sums by finding the missing number.

Good luck!

Welcome to another exciting activity, number detective!

Below is a calculation where both sides should be equal.

However, one of the numbers has been taken away by the cheeky number burglar! Can you work out what it is

11 x 5 =  25 + __

Let's have a go at another one.

Below is a calculation where both sides should be equal.

However, one of the numbers is missing. Can you work out what it is, number detective?

38 + 12 = 35 + __

Below is another calculation where both sides should be equal.

Can you find the number that has been missed out of the sum?

98 - 26 = 21 + __

Below is another calculation where both sides should be equal.

However, one of the numbers has been missed out. Can you work out what it is, number detective?

8 x 5 =  87 - __

Here's another one to have a go at!

Below is a calculation where both sides should be equal.

However, one of the numbers is missing. Can you work out what it is, number detective?

7 x 3 = 90 - __

Here's another one to have a go at, number detective.

Below is a calculation where both sides should be equal.

Can you work out what number has been missed out?

95 - 55 = 10 x __

Below is another calculation where both sides should be equal.

Can you find the missing number, number detective?

59 + 22 = 41 + __

Are you beginning to get the hang of these now?

Below is a calculation where both sides should be equal. Can you find the missing number?

110 - 30 = 10 x __

Only two more to go now, number detective!

Below is a calculation where both sides should be equal.

However, one of the numbers is missing! Can you work out what it is

12 x 2 = 50 - __

You've reached the last question already! Now, don't get over-excited!

Below is a calculation where both sides should be equal.

What's the missing number?

97 - 46 = 94 - __

• Question 1

Welcome to another exciting activity, number detective!

Below is a calculation where both sides should be equal.

However, one of the numbers has been taken away by the cheeky number burglar! Can you work out what it is

11 x 5 =  25 + __

30
EDDIE SAYS
Hi there, detective! How did you get on with one? This question needs to be answered in two steps. First, you need to work out the calculation on the left: 11 x 5 = 55. Then, you have to make the total of the calculation on the right also equal 55. So 25 + __ = 55 can be worked out by doing 55 - 25. The answer to that is 30. Great work!
• Question 2

Let's have a go at another one.

Below is a calculation where both sides should be equal.

However, one of the numbers is missing. Can you work out what it is, number detective?

38 + 12 = 35 + __

15
EDDIE SAYS
Did you get this one? Remember that you need to work through it in two stages. First, you work out 38 + 12 = 50. Then, you have to make the calculation on the right-hand side also equal the number 50. To do this, you need to subtract 35 from 50: 50 - 35 = 15. Just take it carefully, step by step, and you'll get there.
• Question 3

Below is another calculation where both sides should be equal.

Can you find the number that has been missed out of the sum?

98 - 26 = 21 + __

51
EDDIE SAYS
Did you work this one out, number detective? First, you need to do the calculation on the left-hand side of the equals sign: 98 - 26 = 72. Then, you must make the right-hand side also equal 72. To do that, you need to do the sum: 72 - 21. This will give you the answer 51.
• Question 4

Below is another calculation where both sides should be equal.

However, one of the numbers has been missed out. Can you work out what it is, number detective?

8 x 5 =  87 - __

47
EDDIE SAYS
Are you getting the hang of these now? First, you do 8 x 5 = 40. Then, you must make the calculation on the right-hand side also equal 40. So, you do the sum: 87 - __ = 40. This can be worked out by doing 87 - 40 = 47. Remember, take it step by step and you'll get there!
• Question 5

Here's another one to have a go at!

Below is a calculation where both sides should be equal.

However, one of the numbers is missing. Can you work out what it is, number detective?

7 x 3 = 90 - __

69
EDDIE SAYS
You're halfway through this activity! To work out the answer here, you do 7 x 3 = 21. Then, you need to make the right hand side also equal 21. So, you do the sum: 90 - __ = 21 which can be solved by calculating 90 - 21 = 69.
• Question 6

Here's another one to have a go at, number detective.

Below is a calculation where both sides should be equal.

Can you work out what number has been missed out?

95 - 55 = 10 x __

4
EDDIE SAYS
What a lot of missing numbers! For this question, you do 95 -55 = 40. Then, you have to make the right-hand side of the calculation also equal 40. To do this, you have to find out how many tens there are in 40: 40 divided by 10 = 4. Did you get that one?
• Question 7

Below is another calculation where both sides should be equal.

Can you find the missing number, number detective?

59 + 22 = 41 + __

40
EDDIE SAYS
Did you find the missing number this time? First, you need to do 59 + 22 = 81. Then, you have to make the right-hand side also equal 81. This means you have to do the sum: 81 - 41 - you could do this by counting back four tens until you reach the answer, which is 40.
• Question 8

Are you beginning to get the hang of these now?

Below is a calculation where both sides should be equal. Can you find the missing number?

110 - 30 = 10 x __

8
EDDIE SAYS
How did you get on with this one? Don't worry if you're still finding them a bit tricky. Remember that you need to do it in stages and that will make it much easier. So, first, you need to do the left-hand side of the sum: 110 - 30 = 80. Now you have to make the right-hand side also be 80. You can do this by finding out how many tens there are in 80: 80 divided by 10 = 8. So there is your answer - perfect!
• Question 9

Only two more to go now, number detective!

Below is a calculation where both sides should be equal.

However, one of the numbers is missing! Can you work out what it is

12 x 2 = 50 - __

26
EDDIE SAYS
What do we have to do first? The first thing is to do the calculation 12 x 2 = 24. Then, you need to make the right-hand side also equal 24 - we can do this by working out 50 - 24. This gives us the answer 26. Did you get this one right?
• Question 10

You've reached the last question already! Now, don't get over-excited!

Below is a calculation where both sides should be equal.

What's the missing number?

97 - 46 = 94 - __

43
EDDIE SAYS
This looks complicated but it's not difficult so long as you take it in stages. First, do 97 - 46 = 51. Then, you need to make the right-hand side also equal 51, which you can do by subtracting 51 from 94. Did you get the answer of 43? Fantastic work, number detective! You have found all the missing numbers! Very soon we will need your help again on another activity!
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