Measuring temperature
Use negative numbers in context (temperature, finance, sea level); calculate intervals across zero
What a learner can do afterwards
- The temperature falls from 3°C to −5°C — what is the drop? (8 degrees)
- Calculate the difference between a bank balance of −£120 and £350
- Order −7, −3, 0, 2, 5 on a number line and find the interval from −7 to 5
The lesson
You already know that temperatures, bank balances, and sea levels can sit below zero. Now it's time to measure the change between two readings. Count the distance from the start down to zero, then the distance from zero up to the end, and add the two together.
Jay's savings account shows −£120. After a birthday gift, it shows £350. From −£120 to £0 is a change of £120. From £0 to £350 is another £350. £120 + £350 = £470, so his balance changed by £470.
When you cross zero, add the two distances instead of subtracting. Crossing from below zero to above zero (or back) always makes the gap bigger than either number alone.
To measure a change across zero, add the distance down to zero and the distance up from zero.
Watch it
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.