# Deduce the Missing Number in Subtractions Mentally

In this worksheet, students will be asked to use efficient mental methods to subtract mentally. They will use the inverse operation to calculate a missing number.

Key stage:  KS 2

Curriculum topic:   Number: Addition and Subtraction

Difficulty level:

### QUESTION 1 of 10

In this activity, you will be asked to find the missing number in a subtraction question.

The key to this activity is calculating every answer mentally (in your head) without using pen and paper.

Example 1

- 14 = 24

14 + 24 = 38

Check

38 - 14 = 24

Example 2

- 0.6 = 2

Use the inverse operation in order to find the answer:

2 + 0.6 = 2.6

Check

2.6 - 0.6 = 2

Example 3

34 -  = 11

Use the numbers you have been given to complete a subtraction sum in order to find the missing number

34 - 11 = 23

Check

34 - 23 = 11

This method will make more sense when you attempt to answer some questions.

Work out the following equation in your head, in order to find the missing number.

- 55 = 46

Work out the missing number to the equation below, in your head.

- 84 = 112

- 0.7 = 3.0

3.8

3.9

3.7

3.07

- 0.25 = 6.75

7.2

7.0

6.9

7.1

- 0.35 = 8.2

Write the missing number in the blank space below.

7.2

7.0

6.9

7.1

- 324 = 471

Write the missing number in the blank space below.

7.2

7.0

6.9

7.1

Look carefully at the subtraction calculations below.

Each has a missing number, can you match each sum to the correct missing number?

Remember to work mentally.

## Column B

____ - 262 = 411
1,610
____ - 391 = 584
827
____ - 186 = 641
673
____ - 482 = 1,128
975

Look carefully at the subtraction calculations below.

Each has a missing number, can you match each sum to the correct missing number?

Remember to work mentally.

## Column B

____ - 0.4 = 7.0
9.76
____ - 0.45 = 8.0
9.66
____ - 0.66 = 9.1
7.4
____ - 0.66 = 9.0
8.45

Work out in your head, the missing number in the subtraction calculation

2,644 -  = 134

Work out in your head in order to find the missing number in the subtraction calculation.

22.6 -  = 18.2

• Question 1

Work out the following equation in your head, in order to find the missing number.

- 55 = 46

101
EDDIE SAYS
Use the inverse operation, in order to find the answer. 55 + 46 = 101 101 - 55 = 46
• Question 2

Work out the missing number to the equation below, in your head.

- 84 = 112

196
EDDIE SAYS
Again, use the inverse to find the answer. 112 + 84 = 196 196 - 84 = 112 Simple right? Hopefully, this is starting the make sense.
• Question 3

- 0.7 = 3.0

3.7
EDDIE SAYS
3 + 0.7 = 3.7 3.7 - 0.7 = 3.0 This is good, keep it up!
• Question 4

- 0.25 = 6.75

7.0
EDDIE SAYS
Your thought process should have been, 6.75 + 0.25 = 7.0 7.0 - 0.25 = 6.75 Great job if you chose 7.0!
• Question 5

- 0.35 = 8.2

Write the missing number in the blank space below.

EDDIE SAYS
Use the inverse to find the answer. 8.2 + 0.35 = 8.55 8.55 - 0.35 = 8.2
• Question 6

- 324 = 471

Write the missing number in the blank space below.

EDDIE SAYS
471 + 324 = 795 795 - 324 = 471 You’ve got this, keep going...
• Question 7

Look carefully at the subtraction calculations below.

Each has a missing number, can you match each sum to the correct missing number?

Remember to work mentally.

## Column B

____ - 262 = 411
673
____ - 391 = 584
975
____ - 186 = 641
827
____ - 482 = 1,128
1,610
EDDIE SAYS
Use the inverse to find the missing number. These are the correct calculations 673 - 262 = 411 975 - 391 = 584 827 - 186 = 641 1,610 - 482 = 1,128
• Question 8

Look carefully at the subtraction calculations below.

Each has a missing number, can you match each sum to the correct missing number?

Remember to work mentally.

## Column B

____ - 0.4 = 7.0
7.4
____ - 0.45 = 8.0
8.45
____ - 0.66 = 9.1
9.76
____ - 0.66 = 9.0
9.66
EDDIE SAYS
Use the inverse to find the missing number. These are the correct calculations, 7.4 - 0.4 = 7.0 8.45 - 0.45 = 8.0 9.76 - 0.66 = 9.1 9.66 - 0.66 = 9.0
• Question 9

Work out in your head, the missing number in the subtraction calculation

2,644 -  = 134

2510
EDDIE SAYS
You can use the numbers you've already been given in order to complete a subtraction sum. This is how you'll find the missing number. 2,644 - 134 = 2,510 Check your answer! 2,644 - 2,510 = 134
• Question 10

Work out in your head in order to find the missing number in the subtraction calculation.

22.6 -  = 18.2

4.4
4.40
EDDIE SAYS
22.6 - 18.2 = 4.4 Therefore, you can check your answer with the calculation 22.6 - 4.4 = 18.2 Great work, you've completed another activity! How about attempting another one so you feel super confident?
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