Subtracting by Chunking

For example:

45 can be chunked to 40 + 5

126 can be chunked to 100 + 20 + 6

1253 can be chunked to 1000 + 200 + 50 + 3

 

Using Chunking for Subtraction

our sum is

56 - 23 =

this is the same as

50 + 6 - 20 + 3

in order to subtract we need to write the sum vertically

56  =  50 + 6
23  =  20 + 3

Subtract the units first

6 - 3 = 3

then subtract the tens

50 - 20 = 30

then add the answers together

30 + 3 = 33

Another Example

our sum is

158 - 134 =

this is the same as

100 + 50 + 8 - 100 + 30 + 4

in order to subtract we need to write the sum vertically

158  =  100 + 50 + 8
134  =  100 + 30 + 4

subtract the units first

8 - 4 = 4

subtract the tens next

50 - 30 = 20

subtract the hundreds

100 - 100 = 0

add the answers together

0 + 20 + 4 = 24

so

158 - 134 = 24

 

Using chunking with borrowing

our sum is

242 - 128 =

this is the same as

200 + 40 + 2 - 100 + 20 + 8

in order to subtract we need to write the sum vertically

242  =  200 + 40 + 2
128  =  100 + 20 + 8

we need to subtract the units first but we cannot take 8 away from 2

so we need to change the 40 into 30 + 10

we can then add the 10 to the 2 to make 12

242  =  200 + 30 + 12
128  =  100 + 20 + 8

we can now do our sum, starting with the units (including the borrowed 10)

12 - 8 = 4

subtract the tens next

30 - 20 = 10

subtract the hundreds

200 - 100 = 100

add the answers together

100 + 10 + 4 = 114

so

242 - 128 = 114

 

Maths Topics

Place Value    Adding    Number Bonds    Mental Addition    Adding by Chunking    Column Addition    Subtracting    Subtracting by Chunking    Column Subtraction    Mental Subtraction    Roman Numerals

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Page last updated 02/04/2016