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Work Out the Missing Number in Additions in Your Head

In this worksheet, students work out the missing number in addition sums. They try to do the calculations mentally.

'Work Out the Missing Number in Additions in Your Head' worksheet

Key stage:  KS 3

Curriculum topic:  Number

Curriculum subtopic:  Use Relationships Between Operations

Difficulty level:  

Worksheet Overview

QUESTION 1 of 10

In this worksheet, you must work out the missing numbers.

 

Example1

In your head, find the missing number.

26 +
 
= 50

 

Here it is easy to work out the inverse.

50 - 26 = 24

 

Example2

In your head, find the missing number.

-26 +
 
= 50

 

Here we use the inverse again, but be careful about the negative sign.  

50 - -26 = 50 + 26 = 76

 

 

 

Work in your head to find the missing numbers.

20 +
 
= 55

Work in your head to find the missing numbers.

0.2 +
 
= 1

Work in your head to find the missing numbers.

31 +
 
= 100

Work in your head to find the missing numbers.

0.6 +
 
= 1

Work in your head to find the missing numbers.

-27 +
 
= 100

Work in your head to find the missing numbers.

0.26 +
 
= 1

Work in your head to find the missing numbers.

59 +
 
= 100

Work in your head to find the missing numbers.

0.3 +
 
= 1

Work in your head to find the missing numbers.

0.67 +
 
= 1

Work in your head to find the missing numbers.

-20 +
 
= 50
  • Question 1

Work in your head to find the missing numbers.

20 +
 
= 55
CORRECT ANSWER
35
  • Question 2

Work in your head to find the missing numbers.

0.2 +
 
= 1
CORRECT ANSWER
0.8
  • Question 3

Work in your head to find the missing numbers.

31 +
 
= 100
CORRECT ANSWER
69
  • Question 4

Work in your head to find the missing numbers.

0.6 +
 
= 1
CORRECT ANSWER
0.4
  • Question 5

Work in your head to find the missing numbers.

-27 +
 
= 100
CORRECT ANSWER
127
  • Question 6

Work in your head to find the missing numbers.

0.26 +
 
= 1
CORRECT ANSWER
0.74
  • Question 7

Work in your head to find the missing numbers.

59 +
 
= 100
CORRECT ANSWER
41
  • Question 8

Work in your head to find the missing numbers.

0.3 +
 
= 1
CORRECT ANSWER
0.7
  • Question 9

Work in your head to find the missing numbers.

0.67 +
 
= 1
CORRECT ANSWER
0.33
  • Question 10

Work in your head to find the missing numbers.

-20 +
 
= 50
CORRECT ANSWER
70
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