Negative numbers · Usually met around P5
Adding and subtracting on a number line
Add: right. Take away: left. Stop at 0 first.
How to do it
Method
Add: right. Take away: left. Stop at 0 first
3 − 7: 3 → 0 → −4
Another way
Check backwards
−4 + 7 = 3
In full
On a number line, adding a number means moving right and taking one away means moving left. −2 + 5: from −2 move 5 steps right, to 3. 3 − 7: from 3 move 7 steps left: 3 steps take you to 0, then 4 more, to −4. Crossing 0, two moves are quickest: first to 0, then the rest. Check by going back the other way: −4 + 7 = 3, so 3 − 7 = −4 is right.
Worked examples
Have a go first, then open each one for the answer and the working.
Example 1
-9 + 15 = □
Show the answer and working
Answer: 6
From -9 move 15 steps right: 9 of them reach 0, and 6 more reach 6.
Example 2
-10 + □ = 4
Show the answer and working
Answer: 14
Getting from -10 to 4 takes 14 steps right.
Example 3
-4 − 5 = ?
- A. -9
- B. -8
- C. 9
- D. 1
Choose the right answer
Show the answer and working
Answer: A. -9
-4 is already left of 0; 5 more steps left puts it 9 from 0: -9.
Practise it in the game →Negative numbers · Free to start, unlimited questions, no download