Concept 4 of 7
Temperature: Celsius and a Peek at Fahrenheit
Today's big idea
Celsius: 0 freezes, 100 boils, 37 is body heat, and C = (F − 32) × 5/9.
Sign slips cost more than sums, so mark zero before counting the gap.
How it works
👀 What's going on?
A reading of 39 degrees sounds mild in one country and alarming in another. Two different scales are in daily use. Knowing the landmarks on each one keeps you safe.
💡 Here's the trick
Look at the thermometer above. On the Celsius scale water freezes at 0 and boils at 100, and your body sits near 37. On the Fahrenheit scale those same three points read 32, 212 and about 98. Below zero the readings turn negative.
🪄 How to do it
- 1.Mark both readings on the thermometer above.
- 2.Count the gap, adding the two distances when you cross zero.
- 3.To swap scales, use C equals F minus 32, times 5/9.
✍️ Try it
At dawn a hill town reads −6 °C and it rises 11 °C by noon. Then: change 86 °F into Celsius.
Start at −6 and count up 11, which lands on 5 °C. For the second, 86 minus 32 is 54, and 54 times 5/9 gives 30 °C.
⚠️ Watch out
You might be thinking a fall from 4 °C to −4 °C is a fall of 4 degrees. It is 8. Once you cross zero, add the two distances instead of subtracting them.
🌟 Why this matters
You read a temperature to check the weather, bake a cake or look after someone with a fever. Hill stations and freezers both dip below zero, so minus readings are real life.
Exam tip: Sketch a quick scale and mark zero, because sign slips cost more marks than sums do.
Watch me solve one
Quanta solves it
“Watch how I think through one of these — then you try.”
THE PROBLEM
“Temperature drops from 12 °C to −3 °C. By how many degrees?”
- 1
Place both on the integer line
12 above zero, −3 below. 🌡️
- 2
Subtract end from start
12 − (−3)
- 3
Two negatives make plus
= 12 + 3 = 15.
- 4
Answer ✓
The drop is 15 °C.
Now you try one — same steps, different story 👇
See it in action
⚡ Time to play!
Change across zero = distance above 0 + distance below 0. Convert C→F: ×9/5 then +32.
TEMP · ROUND 1 OF 3
5 °C drops to −7 °C
Quick check
✅ VERIFICATION
The temperature rises from −5 °C to 9 °C. By how many degrees did it rise?
⚡ Finish the activity above first to answer.
Keep going!
Up next: Indian Money
Profit = sp − cp (when sp > cp).