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Find the Missing Number to Complete the Sum

In this worksheet, students will complete a calculation by adding in the missing numbers. It will strengthen their number skills.

'Find the Missing Number to Complete the Sum' 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:

19 = 7 + __

One of the numbers is missing.

So 19 is the same as 7 add something.

Now we have two options, we can count on from 7 to 19 or take away 7 from 19 to work out the missing number.

Following either of these options, we find that the missing number is 12.

19 = 7 + 12


 

Let’s try another:

17 = 20 - __

In this question, the answer of 17 is the same as 20 take away something.

What do we need to take away from 20 to reach 17?

So the missing number is 3.

17 = 20 - 3

 

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!

 

Ready, steady, GO ...we're off, number detective!

Below is a calculation. One of the numbers has been taken away by this cheeky little person. Can you work out what the missing number is

 

10 x __ = 120

 

toddler in high chair

Well, here's another calculation with a huge gap in it.  Can you tell what number is missing, number detective?

 

78 - __ = 17

 

baby with one tooth

Below is another delicious calculation. Part of it has disappeared! 

Can you work out what the missing number is, number detective? 

 

88 - __ = 14

 

boy with empty plate

Below is another calculation. One of the numbers has been taken away by the cheeky number burglar! Can you work out what it is, number detective? 

 

5 x __ = 15

 

Get your teeth stuck into this problem, number detective!  One of the numbers in the calculation below has disappeared.

Can you work out what it is? 

 

__ + 20 = 49

 

horse's teeth

You're doing so well, number detective - here's another one to try. Can you find what number is missing from the calculation below?

 

30 + __ = 72

 

lots of question marks

Nearly there!!  Once again, we have a calculation that has a hole in it!

Can you find out what number is needed to fill it in?

 

__ x 5 = 50

 

a black hole

Ready for another challenge, number detective?   Can you work out the missing number in the calculation below?

 

11 + __ = 100

 

boy explorer

Only two more questions to go in this activity!

One of the numbers is missing in the calculation below. Can you work out what it is, number detective? 

 

__ - 20 = 75

 

girl thinking

 

You've reached the final question of this activity. Hooray!

What do you think you've got to do with this one? That's right - you've guessed it - what is the missing number in the calculation below?!

 

88 - __ = 30

 

happy boy

  • Question 1

Ready, steady, GO ...we're off, number detective!

Below is a calculation. One of the numbers has been taken away by this cheeky little person. Can you work out what the missing number is

 

10 x __ = 120

 

toddler in high chair

CORRECT ANSWER
12
EDDIE SAYS
Did you get this first one OK? You need to find out what you multiply 10 by to get 120. The easiest way to do this is to do the reverse calculation of multiplying, which is dividing. So, you could do the sum 120 divided by 10 = 12.
  • Question 2

Well, here's another calculation with a huge gap in it.  Can you tell what number is missing, number detective?

 

78 - __ = 17

 

baby with one tooth

CORRECT ANSWER
61
EDDIE SAYS
Are you getting the hang of these questions? There are several ways to work this one out but probably the easiest is to do 78 - 17. You can break this up into tens and units, so 78 - 10 = 68, then 68 - 7 = 61. Great work!
  • Question 3

Below is another delicious calculation. Part of it has disappeared! 

Can you work out what the missing number is, number detective? 

 

88 - __ = 14

 

boy with empty plate

CORRECT ANSWER
74
EDDIE SAYS
Did you work this one out? The easiest way to find the answer is to do 88 - 14. Broken up into tens and units, this is 88 - 10 = 78, then 78 - 4 = 74. Super!
  • Question 4

Below is another calculation. One of the numbers has been taken away by the cheeky number burglar! Can you work out what it is, number detective? 

 

5 x __ = 15

 

CORRECT ANSWER
3
EDDIE SAYS
How are you doing with these questions - are you getting the hang of them? In this question, you need to find out what to multiply 5 by to get 15. This can be done by a division sum: 15 divided by 5 = 3.
  • Question 5

Get your teeth stuck into this problem, number detective!  One of the numbers in the calculation below has disappeared.

Can you work out what it is? 

 

__ + 20 = 49

 

horse's teeth

CORRECT ANSWER
29
EDDIE SAYS
This might look tricky but it is actually quite a simple one. You could count on from 20 to reach 49 but it is probably easier to do a subtraction sum. You take away 20 from 49, which you work out in jumps of ten - so 49 - 10 = 39. Then 39 - 10 = 29. You're halfway through this number finding mission already!
  • Question 6

You're doing so well, number detective - here's another one to try. Can you find what number is missing from the calculation below?

 

30 + __ = 72

 

lots of question marks

CORRECT ANSWER
42
EDDIE SAYS
You're doing great! Here you need to do the opposite operation to the one in the calculation. The opposite operation of addition is subtraction. So 72 - 30. You can work this out by taking three backwards jumps of ten. So 72 - 10 - 10 -10 = 42.
  • Question 7

Nearly there!!  Once again, we have a calculation that has a hole in it!

Can you find out what number is needed to fill it in?

 

__ x 5 = 50

 

a black hole

CORRECT ANSWER
10
EDDIE SAYS
Again, we need to do the opposite calculation to the one in the question - this means we must use division. We need to find out how many fives there are in 50 so the sum is 50 divided by 5 = 10. Excellent!
  • Question 8

Ready for another challenge, number detective?   Can you work out the missing number in the calculation below?

 

11 + __ = 100

 

boy explorer

CORRECT ANSWER
89
EDDIE SAYS
Did you find the missing number, detective? Once again, you need to do the opposite operation to addition, which is subtraction. So, 100 - 11 = 89. Great work!
  • Question 9

Only two more questions to go in this activity!

One of the numbers is missing in the calculation below. Can you work out what it is, number detective? 

 

__ - 20 = 75

 

girl thinking

 

CORRECT ANSWER
95
EDDIE SAYS
The easiest method here is to use the operation that is opposite to the one given in the calculation. The opposite of subtraction is addition. 75 + 20 can be worked out in two jumps of 10, so 75 + 10 + 10 = 95. Fantastic!
  • Question 10

You've reached the final question of this activity. Hooray!

What do you think you've got to do with this one? That's right - you've guessed it - what is the missing number in the calculation below?!

 

88 - __ = 30

 

happy boy

CORRECT ANSWER
58
EDDIE SAYS
Did you get this final one? To work out the answer here you do 88 - 30. This can be solved as subtracting three jumps of ten. So 88 - 10 - 10 - 10 = 58. Thanks for your help in finding all these missing numbers. Hope to see you again soon!
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