# Subtracting by Chunking

Chunking in mathematics helps pupils to really understand the numbers they are adding as well as helping to develop strategies for mental maths.

Chunking means breaking larger numbers into smaller chunks, separating units, tens, hundreds etc., to make calculations easier.

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

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

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

100 + 10 + 4 = 114

so

242 - 128 = 114