The temperature in the high-altitude desert of Ladakh is recorded as 4 °C at noon. By midnight, it drops by 15 °C. What is the midnight temperature?
Answer: 4 − 15 = −11 °C (11 degrees below zero).
Step-by-step solution
Idea: A drop in temperature is a subtraction. Starting at 4 and going down 15 passes zero, so the answer is negative.
- Midnight temperature = 4 − 15.½ mark
- Going down 4 reaches 0 °C; the remaining 11 degrees take it to −11 °C. So the temperature is −11 °C.½ mark
The midnight temperature is −11 °C.
Check: −11 + 15 = 4 ✓ (rising 15 degrees from −11 °C gets back to 4 °C).
Answer to write in the exam
Midnight temperature = 4 − 15
∴ Midnight temperature = −11 °C
Common mistakes that cost marks
- Writing 15 − 4 = 11 °C and losing the minus sign. The temperature ends below zero.
- Adding instead of subtracting: 4 + 15 = 19 °C. A drop means subtract.
- Writing −19 °C by adding the numbers and then putting a minus sign.
How this can come in the exam
MCQ (1 mark)
At 6 a.m. in Leh it is −8 °C. By noon the temperature rises by 13 °C. The noon temperature is
- −21 °C
- 5 °C
- −5 °C
- 21 °C
Show answer
(B) 5 °C
−8 + 13 = 5 °C.
Short answer (2 marks)
The temperature at Dras was −6 °C at 8 p.m. It fell by 3 °C every hour until midnight. Find the temperature at midnight.
Show answer
8 p.m. to midnight is 4 hours, so the fall is 4 × 3 = 12 °C (1 mark). Temperature = −6 − 12 = −18 °C (1 mark).Try one yourself
A freezer is at −18 °C. During a power cut its temperature rises by 25 °C. What is its new temperature?
Show answer
−18 + 25 = 7 °C.
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