Subtraction.
1) Number line work
Counting back in tens then the units.
84 - 33 = 51
-3
-10
51
54
-10
64
73 – 28 = 45
-5 -3
45 50
-10
74
-10
53
84
-10
63
2) Subtraction by partitioning.
Example 1
1 5 7 - 4 5
1 0 0
5 0
7
4 0
5
1 0 0 + 1 0 + 2 = 1 1 2
73
Children can make
this method more
efficient by
making their jumps
larger. For
instance, by
jumping back 30 in
the example given.
In the second
example the 8
units are taken
away in two
chunks. The first
of 3 to get to the
50 then the 5 to
complete the sum.
For this method it
is important that
children line up
the units, tens and
hundreds.
The addition signs
are not put into
the numbers when
they are first
partitioned.
Example 2
7 7 9 - 2 5 6
7 0 0
7 0
9
- 2 0 0
5 0
6
5 0 0 + 2 0 + 3 = 5 2 3
3) Subtraction by partitioning involving
exchanging of tens and hundreds.
Example 1.
8 5 4 - 2 2 8
4
0
8 0 0
5 0 1 4
- 2 0 0
2 0
8
6 0 0 + 2 0 + 6 = 6 2 6
Example 2
9 2 3 - 6 6 7
8
0
0
1
1
0
9 0 0
2 0 1 3
- 6 0 0
6 0
7
2 0 0 + 5 0 + 6 = 2 5 6
Children should be
encouraged to
subtract the units
first as this will
prepare them for
column methods of
subtraction.
The sum is ‘set up’
before any
subtraction is
carried out.
In example 1 the
units are the
problem. The 50 is
partitioned into 40
+ 10 and the 10 is
then exchanged
into the units’
column.
In example 2, both
the units and the
tens are problems.
All the exchanging
is done, starting
with the units,
before the
subtraction is
carried out.
4) Standard written method
Example 1
6 5 3 -
2 2 8
4
6 5 13
- 2 2 8
4 2 5
Example 2
3 4 3 8
2
- 8 5 2
13
3 4 13 8
8 5 2
2 5 8 6
As with the
previous method, all
the exchanging is
carried out and the
sum is ‘set up’,
before any
subtraction takes
place.