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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!

 

 

 

 

 

Hi there, 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

 

 77 + 13 = 100 - __

 

Here's another 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? 

 

75 - 63 = 3 x __

 

girl and magnifying glass

Are you ready for another challenge, number detective?

Below is a calculation where both sides should be equal. 

Can you work out what the missing number is?

 

11 x 10 = 13 + __

girl with telescope

Yippee ... another wonderful sum to do!

Below is a calculation where both sides should be equal. 

Can you work out what has been missed out, number detective?

 

6 x 4 =  96 - __ 

 

police station

Halfway there already, number detective.

Below is a calculation where both sides should be equal. 

Can you work out what is the missing number?

6 x 11 = 33 +  __

 

children thinking

Below is another calculation where both sides should be equal. 

Can you work out the missing number?

46 + 32 = 41 + __

 

question mark

Don't give up, number detective - you're nearly there!

Below is a calculation where both sides should be equal. 

Can you work out what number is missing?

 

47 - 38 = 3 x  __

 

hole

You've guessed it - below is a calculation where both sides should be equal. 

Can you work out what number is missing?

 

 60 - 35 = 5 x __

 

binoculars

The last two questions coming up!

Below is a calculation where both sides should be equal. 

Can you use your detecting skills to work out what number is missing?

 

78 + 21 = 11 x __

 

empty plate

 

Now don't get over-excited just because this is the final question in this activity!

Below is a calculation where both sides should be equal. 

Just for a change, can you find out what the  missing number is?

 

101 - 41 = 22 + __

 

laughing children

  • Question 1

Hi there, 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

 

 77 + 13 = 100 - __

 

CORRECT ANSWER
10
EDDIE SAYS
Some fun and challenging questions in this activity! There are two steps to take in order to find the missing number. First, work out the answer to the calculation on the left. So 77 + 13 = 90. Then, you need to make sure that the answer to the sum on the right-hand side is also equal to 90. So, we know that 100 take away our mystery number must equal 90. Therefore, the sum we need to do is: 100 - 90 = 10. Did you follow all that?
  • Question 2

Here's another 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? 

 

75 - 63 = 3 x __

 

girl and magnifying glass

CORRECT ANSWER
4
EDDIE SAYS
Right, let's see how to work this one out. You will find it much easier if you take it slowly, in stages. First, work out 75 - 63 = 12. Then, you must make sure that the answer to the right-hand side is also 12. You know that 3 x __ = 12, so we can work out the mystery number by finding how many threes there are in 12: 12 divided by 3 = 4.
  • Question 3

Are you ready for another challenge, number detective?

Below is a calculation where both sides should be equal. 

Can you work out what the missing number is?

 

11 x 10 = 13 + __

girl with telescope

CORRECT ANSWER
97
EDDIE SAYS
Did you work this one out, detective? First, you need to do 11 x 10 = 110. Then, make sure you get the same answer on the right-hand side. We know that 13 +_ = 110 so, we can work out what the mystery number is by doing 110 - 13. Wonderful - we have our answer of 97!
  • Question 4

Yippee ... another wonderful sum to do!

Below is a calculation where both sides should be equal. 

Can you work out what has been missed out, number detective?

 

6 x 4 =  96 - __ 

 

police station

CORRECT ANSWER
72
EDDIE SAYS
Are you getting the hang of this yet? To find the answer you have to work out 6 x 4, which equals 24. Now you know that the right-hand side will also equal 24. So, 96 - __ = 24 can be worked out by doing 96 - 24 to find the answer is 72!
  • Question 5

Halfway there already, number detective.

Below is a calculation where both sides should be equal. 

Can you work out what is the missing number?

6 x 11 = 33 +  __

 

children thinking

CORRECT ANSWER
33
EDDIE SAYS
How did you do? First, do 6 x 11 = 66. Then, to make the right-hand side also equal 66, you need to do the sum 66 - 33. Which gives us the lovely neat answer of 33!! Five numbers found, five more to go, number detective!
  • Question 6

Below is another calculation where both sides should be equal. 

Can you work out the missing number?

46 + 32 = 41 + __

 

question mark

CORRECT ANSWER
37
EDDIE SAYS
Did you get this one? First, you work out 46 + 32 = 78. Then, 41 + __ = 78 can be worked out by doing 78 - 41. Whoosh! You're whizzing through these questions!
  • Question 7

Don't give up, number detective - you're nearly there!

Below is a calculation where both sides should be equal. 

Can you work out what number is missing?

 

47 - 38 = 3 x  __

 

hole

CORRECT ANSWER
3
EDDIE SAYS
How did you do? First, you work out 47 - 38 = 9. Then, 3 x __ = 9 can be solved by working out how many threes there are in 9. It then becomes a simple test of your three times table knowledge!
  • Question 8

You've guessed it - below is a calculation where both sides should be equal. 

Can you work out what number is missing?

 

 60 - 35 = 5 x __

 

binoculars

CORRECT ANSWER
5
EDDIE SAYS
You're finding so many of our missing numbers! This time, you need to work out 60 - 35 = 25. Then, 5 x __ = 25 can be solved by working out how many fives there are in 25. Are you good at your five times table? If so, then this would have been an easy question to solve: 25 divided by 5 = 5!
  • Question 9

The last two questions coming up!

Below is a calculation where both sides should be equal. 

Can you use your detecting skills to work out what number is missing?

 

78 + 21 = 11 x __

 

empty plate

 

CORRECT ANSWER
9
EDDIE SAYS
How are you getting on, number detective? You need to work out 78 + 21 = 99. Then, you need to find out what you multiply 11 by to get the same answer of 99. So, how many elevens are there in 99? The answer is 9! Are you ready for the last question?
  • Question 10

Now don't get over-excited just because this is the final question in this activity!

Below is a calculation where both sides should be equal. 

Just for a change, can you find out what the  missing number is?

 

101 - 41 = 22 + __

 

laughing children

CORRECT ANSWER
38
EDDIE SAYS
How did you do with this last one? This time, you work out 101 - 41 = 60. Then, 22 + __ = 60 can be solved by doing 60 - 22. This activity is now complete!! Well done for doing all that hard work, number detective.
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