Arithmetic Grade Four

Lesson Thirty-eight: Subtraction Chains

Information:
A common shortcut which you might consider trying is to add all the small numbers and subtract their sum from the big number. In other words,

    33 - 5 - 4 - 12 - 3

is the same as

    33 - (5 + 4 + 12 + 3)

To solve this problem we must first add the numbers in the parentheses:

    5 + 4 + 12 + 3 = 24

Then we subtract this sum from 33.

    33 - 24 = 9
Some people will find it easier to do this addition first and then subtracting once, while other people will prefer to just subtract each number from left to right.

Here's another example: 


     66 - 15 - 12 - 21 - 9

We reorganize the problem like this:

     66 - ( 15 + 12 + 21 + 9 )

Add the numbers in the parentheses:

     15 + 12 + 21 + 9 = 57

Subtract 57 from 66 and we get 9 as our final answer.

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