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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.

'Complete the Sum to Find the Missing Number' worksheet

Key stage:  KS 2

Curriculum topic:   Verbal Reasoning

Curriculum subtopic:   Complete the Calculation

Difficulty level:  

Worksheet Overview

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.

boy on computer

 

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

 

Pssstt!! Here’s a handy hint to help you reach superstar status:

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!

 

 

 

 

 

Hello number detective and welcome to another wonderful worksheet on numbers!

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? 

 

 156 - 49 = 66 + __ 

 

Let's try another one!

Below is a calculation where both sides should be equal. 

Can you work out what number has been missed out?

 

24 ÷ 6 =  16 ÷ __

 

 

Below is another calculation where both sides should be equal. 

Can you use your great detecting skills to work out what number has been missed out?

 

 185 - 91 = 190 - __

boy thinking

Ready for another challenge, number detective?

Below is a calculation where both sides should be equal. 

What number has been missed out?

 

80 ÷ 5 = 2 x __ 

 

 

Halfway there, word detective!

Below is a calculation where both sides should be equal. 

Can you work out what the missing number is?

 

8 x 11 = 218 - __

 

question mark

Below is a calculation where both sides should be equal. 

Can you work out what the mystery number is? 

 

 42 ÷ 3 = 2 x __

 

 

Keep going, number detective - you are so nearly there!

Below is a calculation where both sides should be equal. 

Can you find what number has been missed out?

 

88 + 77 = 95 + __

 

 

Below is yet another calculation where both sides should be equal! 

Can you help us out again and find the mystery number?

 

13 x 5 = 200 - __

 

children thinking

The last two questions coming up, number detective!

Below is a calculation, where both sides should be equal. 

Can you see what number has been missed out?

 

81 + 79 =  80 + __

 

 

 

Well done, you've reached the final question, number detective!

Below is a calculation where both sides should be equal. 

Can you work out what the mystery number is?

 

13 x 10  =  82 + __

 

boy flexing muscles

  • Question 1

Hello number detective and welcome to another wonderful worksheet on numbers!

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? 

 

 156 - 49 = 66 + __ 

 

CORRECT ANSWER
41
EDDIE SAYS
Did you find the first missing number, detective? First, you need to work out 156 - 49 =107. Then, you add 107 to the sum on the right-hand side: 66 + __ = 107. This can be solved by doing 107 - 66 = 41. Just take it slowly and work through it in stages.
  • Question 2

Let's try another one!

Below is a calculation where both sides should be equal. 

Can you work out what number has been missed out?

 

24 ÷ 6 =  16 ÷ __

 

 

CORRECT ANSWER
4
EDDIE SAYS
This one is a bit easier, so long as you know your times tables! First, you work out 24 ÷ 6 = 4. Then, add the 4 on to the right-hand side: 16 ÷ __ = 4. This can be worked out by doing 16 ÷ 4. Great, let's find some more numbers!
  • Question 3

Below is another calculation where both sides should be equal. 

Can you use your great detecting skills to work out what number has been missed out?

 

 185 - 91 = 190 - __

boy thinking

CORRECT ANSWER
96
EDDIE SAYS
How did you do, number detective? First, do 185 - 91 = 94. Then, 190 - __ = 94 can be worked out by doing 190 - 94. Excellent!
  • Question 4

Ready for another challenge, number detective?

Below is a calculation where both sides should be equal. 

What number has been missed out?

 

80 ÷ 5 = 2 x __ 

 

 

CORRECT ANSWER
8
EDDIE SAYS
Top effort! First of all, do 80 ÷ 5 = 16. Then 2 x __ = 16 can be worked out by doing the opposite operation to multiplication (division). So the calculation will be 16 ÷ 2, which equals 8. Terrific!
  • Question 5

Halfway there, word detective!

Below is a calculation where both sides should be equal. 

Can you work out what the missing number is?

 

8 x 11 = 218 - __

 

question mark

CORRECT ANSWER
130
EDDIE SAYS
Let's work it through slowly. First, do 8 x 11 = 88. Then 211 - __ = 88 can be solved by doing 218 - 88. Remember you can count back in blocks of ten, then units. You've found five numbers, can you help us find the remaining five?
  • Question 6

Below is a calculation where both sides should be equal. 

Can you work out what the mystery number is? 

 

 42 ÷ 3 = 2 x __

 

 

CORRECT ANSWER
7
EDDIE SAYS
First, do 42 ÷ 3 = 14 as there are fourteen threes in 42. Then 2 x __ = 14 can be solved by doing the opposite operation to multiplication (division). So the sum will be 14 ÷ 2. Super!
  • Question 7

Keep going, number detective - you are so nearly there!

Below is a calculation where both sides should be equal. 

Can you find what number has been missed out?

 

88 + 77 = 95 + __

 

 

CORRECT ANSWER
70
EDDIE SAYS
How did you do, are you getting the hang of this? First, you need to do 88 + 77 = 165. Then, 95 + __ = 165 which can be solved by doing 165 - 95. Fantastic work, number detective!
  • Question 8

Below is yet another calculation where both sides should be equal! 

Can you help us out again and find the mystery number?

 

13 x 5 = 200 - __

 

children thinking

CORRECT ANSWER
135
EDDIE SAYS
Nice work detective! The first step is to do 13 x 5 = 65. Then, 200 - __ = 65 can be solved by doing 200 - 65, which is 135. Are you feeling more confident with these now?
  • Question 9

The last two questions coming up, number detective!

Below is a calculation, where both sides should be equal. 

Can you see what number has been missed out?

 

81 + 79 =  80 + __

 

 

 

CORRECT ANSWER
80
EDDIE SAYS
Did you find the missing number, detective? First of all, you need to do 81 + 79 = 160. Then 80 + __ = 160 can be solved by doing the opposite operation to the one used in the question. The opposite of addition is subtraction, so the sum will be 160 - 80.
  • Question 10

Well done, you've reached the final question, number detective!

Below is a calculation where both sides should be equal. 

Can you work out what the mystery number is?

 

13 x 10  =  82 + __

 

boy flexing muscles

CORRECT ANSWER
48
EDDIE SAYS
How did you do on this last question? First of all, you have to work out 13 x 10 = 130. Then, 82 + __ = 130 can be solved by doing 130 - 82. What a number expert, you've tracked down all the missing numbers! We hope to see you again soon!
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