Transcript Slide 1

Using number lines
in Addition and
Subtraction
By Lucy Ralph 2013
Adding numbers using
the number line.
25
47
So how do we do this using
the number line?
We use the strategy called:
Counting Up
You need to think about:
What number shall I start with on my
number line?
What number do we want to count up by?
Are there any number bonds that can help
me?
25 + 47 =
Use the counting up method!!
+20
+3
47
67
+2
70 72
So we start at the biggest number…47
And count up 25 places
What number do we end on???
So….
25 + 47 =
72
?
+ 34 = 57
Use the Counting
Strategy
Up
Remember -You need to think about:
What number shall I start with on my
number line?
What number do we want to count up by?
Are there any number bonds that can help
me?
+ 34 = 57
+10
+10
34
+3
44
54
34
So what is
10 + 10 + 3 = 23
So…..
23
+
34 = 57
57
57
Can I use the counting up
strategy for Subtraction too?
YES
Have a look at this question!
43 – 27 =
16
What number shall I start from on my number line?
What number do I want to get to?
What number shall count on by?
Can any number bond make counting on easier for me?
+10
27
10 + 3 + 3 = 16
+3
37
+3
40
43
32 -
= 18
What number shall I start from on my number line?
What number do I want to get to?
What number shall count on by?
Can any number bond make counting on easier for me?
+10
+2
+2
18
20
30
2 + 10 + 2 = 14
So….
32 -
14
= 18
32
Have a go at these questions now using number lines
and the counting on strategy:
1.
2.
3.
4.
5.
45 – 25 =
54 – 26 =
– 19 =36
28 –
= 14
43 – 37 =
6.
55 + 18 =
7.
29 + 40 =
8.
33 +
9.
= 51
+ 14 = 35
10. 22 + 15 =
Extra for Experts:
1. 154 – 147
6.
123 + 19
2. 172 – 133
7.
199 + 98
3. 198 – 188
8.
147 + 76
4. 134 – 119
9.
201 + 97
5. 176 - 134
10. 185 + 89
Work out the following
calculations mentally:
•
•
•
•
43 – 37
102 – 98
154 – 147
3005 – 2997
How can we show this using the
number line:
43 – 37
+3
+3
37
3+3=6
So,
40
43 – 37 = 6
43
154 – 147
+4
+3
3+4=7
So,
147
150
154
154 – 147 = 7
Have a look at these Calculations
• 144 – 138
• 89 – 34
What is it about the numbers that
made you decide to use mental
method or a number line?
• 134 – 123
• 125 - 76
Do you always need to use a number
line when the numbers are a
long way apart??
- 285 = 39
+
+
285
300