| Positive and Negative Numbers
Number line: -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10
This is a section of the number line from –10 to + 10.
Note, we can write positive numbers without the + sign.
With these numbers, we will have double signs: + –, + +, – – and – +.
It is easier to replace these with single signs: + or –.
– + can be replaced with –.
+ + or – – can be replaced with +.
Example 1:
6+ – 4 = 6 – 4 = 2
6 – + 4 = 6 – 4 = 2
6 + + 4 = 6 + 4 = 10
6 – – 4 = 6 + 4 = 10
Rule: If the double signs are different, they are –.
If they are the same, they are +.
We can now add and subtract on the number line.
Example 2:
4 – 7 = –3
We start at 4 on the number line and move 7 places to the left, as illustrated below.
-7 - 6 - 5 - 4 - 3 - 2 - 1 0 1 2 3 4 5 6 7
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End _________Start
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Move 7 |
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–3 + 7 = 4
We start at –3 and move 7 places to the right, as shown below.
-4 -3 -2 -1 0 1 2 3 4 5 6
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Move 7
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–1 – 5 = –6
We start at –1 and move 5 to the left.
Rule: Start with the first number and move right for + and left for – .
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