In this section we look at adding and subtracting when negative numbers are involved.
We will use a number line like the one below to help us.
If you subtract a positive number you move to the left on a number line. Always start from the position of the first number. | |
3 + 5 = 8 (start at 3 and move 5 to the right) -4 + 5 = 1 (start at -4 and move 5 to the right) -9 + 5 = -4 (start at -9 and move 5 to the right) | 9 - 7 = 2 (start at 9 and move 7 to the left) 3 - 7 = -4 (start at 3 and move 7 to the left) -1 - 7 = -8 (start at -1 and move 7 to the left) |
Practice Questions
Work out the answer to each of these questions then click on the button marked
to see whether you are correct.
(a) -3 + 8 | |
(b) -8 + 5 | |
(c) 5 - 7 | |
(d) -2 - 3 |
We can also use a number line when adding or subtracting negative numbers.
If you subtract a negative number you move to the right on a number line. Again, start the movement from the position of the first number. | |
7 + (-4) = 3 (start at 7 and move 4 to the left) 1 + (-4) = -3 (start at 1 and move 4 to the left) -3 + (-4) = -7 (start at -3 and move 4 to the left) | 4 - (-3) = 7 (start at 4 and move 3 to the right) -2 - (-3) = 1 (start at -2 and move 3 to the right) -8 - (-3) = -5 (start at -8 and move 3 to the right) |
Practice Questions
Work out the answer to each of these questions then click on the button marked
to see whether you are correct.
(a) 4 + (-2) | |
(b) -1 + (-3) | |
(c) 4 - (-2) | |
(d) -5 - (-3) |
This table may help you remember the rules:
Adding a positive - move right | Subtracting a positive - move left |
Adding a negative - move left | Subtracting a negative - move right |
you start with a positive or negative number |
 
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