Revision notes
Understand negative numbers, compare them, and add and subtract using the number line.
In Jos, a harmattan night can be 8°C. A freezer is colder still: about −18°C — that's 18 degrees BELOW zero. Numbers below zero are called negative numbers, and you use them for temperatures, bank balances and even floors below ground level in a building.
Integers are the whole numbers, their negatives, and zero: … −3, −2, −1, 0, 1, 2, 3 …
On a number line, positive numbers are to the RIGHT of zero and negative numbers are to the LEFT.
The further LEFT a number is, the SMALLER it is. So −7 is smaller than −2, even though 7 is bigger than 2.
🔑 Key idea: Right = bigger. Left = smaller.
−3 + 5
Step 1: Start at the first number
Put your finger on −3 on the number line.
Step 2: Move 5 to the right
From −3, count 5 steps right.
You land on 2.
Why? Right means bigger (more positive). Left means smaller (more negative).
Answer: 2
Subtracting a positive number moves you LEFT: 2 − 6 = −4.
But what about 4 − (−3)? Think of money: taking away a ₦300 debt leaves you ₦300 better off.
So subtracting a negative is the same as adding: 4 − (−3) = 4 + 3 = 7.
🔑 Key idea: Two minus signs side by side make a plus: − (−) = +
4 − (−3)
Step 1: Start at the first number
Put your finger on 4 on the number line.
Step 2: Two minus signs make a plus
4 − (−3) = 4 + 3
Why? Taking away a debt is the same as being given money: subtracting a negative means adding.
Step 3: Move 3 to the right
From 4, count 3 steps right.
You land on 7.
Why? Right means bigger (more positive). Left means smaller (more negative).
Answer: 7
Ready to check you've got it? Scroll up and work through the lesson: the interactive visuals, practice questions and mastery check are all there.