Download Subtraction

I think of a number and add 6.
My answer is negative 7, what number did I start with?
Sums and
Things for
Parents
Negative 13
Well done Lucie.
How did you think that through?
Sums and
Things for
Parents
The story so far ……….
 children’s recall of number facts
has become more accurate and faster
 children are more aware of the strategies
they use to calculate
 they use vocabulary correctly
 they are more confident about maths
 maths is more fun!
What can a numerate child do?
By the age of 11 they should :

have a sense of the size of number and
where it fits into the number system

know by heart addition and subtraction
facts to 20, multiplication and division
facts to 10x10, doubles and halves,
complements to 100, multiply and
divide by 10 and 100

use what they know to figure out
answers mentally
What can a numerate child do? (cont.)

calculate accurately and efficiently, both
mentally and on paper, using a range
of strategies

recognise when it is appropriate to use a
calculator- and when it is not- and be
able to use one effectively

explain their methods and reasoning
using correct mathematical terms

judge whether their answers are
reasonable and have strategies for
checking them where necessary
The aim
 The aim is for children to do mathematics in
their heads, and if the numbers are too
large, to use pencil and paper to avoid
losing track. To do this children need to
learn quick and efficient methods,
including appropriate written methods.
Learning written methods is not
the ultimate aim.
 Mathematics is foremost an activity of the
mind, and written calculations are an aid
to that mental activity.
 The Numeracy Strategy aims to develop
children’s mental strategies and then
written methods that derive from and
support mental methods.
We want children to ask
themselves:
Can I do this in my head?
Can I do this in my head using drawings or
jottings?
Do I need to use an expanded/compact
written method?
Do I need a calculator?
How do you add and subtract?
61 + 45
7800 – 5600
5735 + 3657
5735 + 3990
83 – 68
5002 – 4996
538 - 295
267 + 267
2.5 + 2.7
5.1 - 2.78
Mistakes children make:
1
16
-
9
…….and more:
643
6
10
13
803
+ 274
- 526
8117
187
Addition
76 + 47 =
+10
76
+10
86
+10
96
+10
106
+7
116
+ 40
76
123
+7
116
123
Addition
358 + 473 =
358
358
+ 473
+ 473
11
120
831
700
831
1
1
Addition
176 + 147 =
100 + 70 + 6
+ 100 + 40 + 7
200 + 110 + 13
= 323
Subtraction
Imran has 43 conkers; he gives 24 away to his
friends. How many does he have left?
43 – 24 =
19 20
-1
19 conkers
23
-3
33
-10
43
-10
Subtraction
Sam has saved 93p, Amy has 55p. How much
more money does Sam have than Amy?
93 – 55 =
+5
55
38p more
+30
60
+3
90
93
Subtraction
8.23 – 4.55 =
+0.45
4.55
3.68
5.00
+3
+0.23
8.00
8.23
Subtraction
A sports stadium holds 9010 spectators. 5643
people attend a football match. How many
empty seats are there?
+ 57
5643
5700
+300
+3010
6000
9010
5643
3367 empty seats
5700
6000
9010
57
+300
+3010
3367
How do you multiply and
divide?
57 x 2
78 ÷ 2
43 x 50
742 ÷ 2
36 x 25
700 ÷ 4
18 x 15
65.5  10
8 x 19
17 ÷ 5
34 x 7
5.4 ÷ 6
Mistakes children make:
76
67
8
x 54
5648
268
x
335
101 r 5
7 847
603
Multiplication
47 x 8 =
x
8
40
320
7
56
30
1200
180
7
280
42
376
37 x 46 =
x
40
6
1480
222
1702
……… leading to algebra at KS3
(a + b)
2
= (a + b) x (a + b)
x
a
b
a
2
a
ab
b
ab
2
b
2
a + ab
2
ab + b
2
a + 2ab + b
(a + b)
2
2
= a + 2ab + b
2
2
Division
47  8
375  43
8
47
43 375
…or ‘chunking’
First on a number line
3
87 ÷ 7
17
87
-14
subtract 7x2 or 7 twice
-70
subtract 7x10 or 7 ten times
We have subtracted seven
12 times and have 3 left
so… 87 ÷ 7 = 12 r 3
A shop notice states that there are 87 shopping
days to Christmas. How many weeks is that?
87
-70
(10 weeks)
17
-14
(2 weeks)
3
So it’s 12 weeks (and 3 days) of shopping to
Christmas.
432 school children are going on an outing. If
each bus takes 15 passengers, how many buses
will be needed?
432
-300
132
(20 buses)
- 90
(6 buses)
42
-30
(2 buses)
12
(people left)
So we need 29 buses or 28 buses and some
cars!
How can you help?
Talk about
how you
do maths
Give praise and
encouragement
Be positive
Ask your
child to
explain
Make sure maths is fun!