Work Out the Missing Number in Additions in Your Head

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

 

Example 1

In your head, find the missing number.

26 +

=

50

 

Answer

Here it is easy to work out the inverse.

50 - 26 = 24

 

 

Example 2

In your head, find the missing number.

-26 +

=

50

 

Answer

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

50 - -26 = 50 + 26 = 76

 

 

Example 3

In your head, find the missing number.

0.81 +

=

1

 

Answer

Here it is easy to work out the inverse.

1 - 0.81 = 1.00 - 0.81 = 0.19

It may help to think of 100 - 81 = 19.