In a horizontal number line:
1. When adding, start from the first number, count right along the number line.
2. When subtracting, start from the first number, count left alone the number line.
Note:
In a horizontal number line, numbers to the right of zero are positive, and numbers to the left are negative.
Example 4
Use number line to find the value of:
i. 0 +Â 6
ii. 2 +Â 7
iii. -6Â –Â 4
iv. -8Â +Â 11
v. -5 Â +Â 4
vi. -3Â –Â 5
Solution
i. 0 Â + Â 6
 *Start at 0, count 6 places to the right to end up at 6.
So, 0 + 6 = 6
ii. 2 Â + Â 7 Â
 *Start at 2, count 7 places to the right to end up at 9.
So, 2 + 7 = 9.
 iii. -6 – 4
*Start at -6, count 4 places to the left to end up at -10.
So, -6 -4 = -10.
iv. -8 Â +Â 11
*Start at -8, count 11 places to the right to end up at 3.
v. -5Â Â + Â Â 4
*Start at -5, count 4 places to the right to end up at -1.
vi. Â -3Â –Â 5
*Start at -3, count -5 places to the left to end up at -8.
So, -3 – 5 = -8
Note:Â
The -ve sign directs the number to the left while the +ve directs the number to the right.
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