Checking Subtractions (1)

From any addition fact such as

35 + 23 = 58

 

we can work out two subtraction facts.

 

Here we get

58 - 35 = 23

and

58 - 23 = 35

 

This is handy because we can use additions to check subtractions.

 

 

Example 1

Anna says that

 

33 - 15 =     18     

 

Use addition to check if she is right or wrong.

 

Answer

18 + 15 = 33

 

So Anna is right.

 

 

Example 2

Ben says that

 

54 - 15 =     31     

 

Use addition to check if he is right or wrong.

 

Answer

31 + 15 = 46 not 54

 

So Ben is wrong.