Thermometer: Reading Temperature

Today's big idea

A rise is an addition and a fall is a subtraction, whatever the scale shows.

Degrees of change and degrees on the tube are two different numbers.

How it works

👀 What's going on?

Open a window on a cold morning and the room drops a few degrees. A thermometer is the tool that puts a number on how hot or cold something is.

💡 Here's the trick

Look at the thermometer above. The red column stops at 30, so the temperature right now is 30°C. It then rises by 8°C, and the working beside it adds: 30 + 8 = 38°C. A rise is an addition and a fall is a subtraction. Ice melts at 0°C and water boils at 100°C. A warm room is about 25°C, and a fever is about 40°C.

🪄 How to do it

1.Read the top of the red column on the thermometer above.
2.Write down the change, and whether it is a rise or a fall.
3.Add for a rise, subtract for a fall.

✍️ Try it

1.At 7 am a city is 14°C. By noon it has risen 11°C. What is the noon temperature?
2.A room is 22°C. A fan cools it by 7°C, then the evening cools it another 6°C. What is it now?

A rise means add, so the city reaches 14 + 11 = 25°C at noon. The room falls twice: 22 − 7 = 15°C after the fan, then 15 − 6 = 9°C by evening.

⚠️ Watch out

You might be thinking that "cooler by 12°C" means the answer is 12°C. It does not. Starting at 30°C and cooling by 12°C gives 30 − 12 = 18°C. The 12 is the size of the drop, never the new reading.

🌟 Why this matters

You read a temperature to choose a jacket, to check a fever, and to know when an oven is ready. A parent hears 39°C and worries, while 37°C is perfectly normal. Saying how far a number moved is the part that actually helps.
Exam tip: Sketch a tiny number line for two-step changes so a rise and a fall never get swapped.

Watch me solve one

Quanta solves it

“Watch how I think through one of these — then you try.”

THE PROBLEM

“The temperature is 25°C. It rises by 8°C. What is the new temperature?”

1
Read the level
Starting temperature = 25°C.
2
Rise = add
25 + 8 = 33
3
Answer ✓
New temperature = 33°C

Now you try one — same steps, different story 👇

See it in action

⚡ Time to play!

Set the mercury to 37°C — a healthy body temperature.

TEMPERATURE · ROUND 1 OF 3

READING

20°C

target 37°C

Quick check

✅ VERIFICATION

It was 9°C at dawn and 26°C at noon. By how much did the temperature rise?

⚡ Finish the activity above first to answer.

Keep going!

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