lesson
Cross zero in two parts
1 · Learn
Negative values lie below zero. On a number line increasing to the right, -3 is greater than -8. The size of the digit alone does not order negative numbers.
For a distance across zero, count up to zero and then onwards. A temperature change has direction as well as size; a rise of 9 degrees is different from a final temperature of 9 degrees.
2 · Worked example
From -5°C to 7°C is a rise of 5 + 7 = 12°C. The final temperature is 7°C, not 12°C.
3 · Your turn
Find the rise from -9°C to 4°C. Then find the temperature after 4°C falls by 7°C.
Check your answer
A rise of 13°C; the later temperature is -3°C.
4 · Apply your learning
Draw both journeys on a labelled number line and distinguish a position from an interval.
Adult guidance and safety
Ask the learner to explain the method and check it using a different representation. Supply place-value grids, fraction strips, accurate diagrams and measuring tools where needed. These examples need varied practice; a short correct answer alone does not establish fluency.
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