The note
How schools teach it now
Taught with a number line, often an upright one like a thermometer. Children count on and back across zero. Rules such as 'two minuses make a plus' come later, at secondary school, so don't start with them.
5-minute kitchen-table activity
Draw a thermometer from −10 to 10 on a strip of paper. Ask: 'It's −3°C at night and warms up by 8 degrees. What is it now?' (5°C.) Then look up a cold city on the weather app and compare.
Worked example
At 6 am it was −4°C. By noon it was 7°C. How many degrees did the temperature rise?
- From −4 up to 0 is 4 degrees.
- From 0 up to 7 is 7 degrees.
- 4 + 7 = 11.
Answer: 11 degrees
Common mistakes to watch for
- Answering 3 (7 − 4) by ignoring the minus sign.
- Thinking −8 is bigger than −2 because 8 is bigger than 2.
- Counting the starting number as a jump on the number line.
Encouragement
- Try saying
- “Let's jump to zero first, then on from there.”
- Rather than
- “Negatives are just hard, don't worry about them.”