A temperature of −6°C rises by 9°C. Find the new temperature.
Incorrect answer: −15°C
A negative result is not automatically an error. It can represent debt or a location below a reference level. But distance between two positions is nonnegative.
Moving the wrong way with negative numbers
A rise moves right on a number line even when the starting value is negative. A decrease can cross zero.
The correction
3°C
−6 + 9 = 3.
- Identify the starting value, the change, and the quantity being asked for.
- Write an equation with signs and consistent units before calculating.
- Check whether the result fits the story; distinguish a signed position from a positive distance.
Try the reasoning in another example
A balance is $12.50. A $16.75 charge is applied. What is the new balance?
- A charge decreases the balance: 12.50 − 16.75.
- The charge exceeds the balance by 4.25.
Answer: −$4.25
Explain why each step preserves the quantity or relationship. If you can compute the answer but cannot explain the step, revisit the model before adding more questions.
The short check below reuses the first example as a retrieval question and adds a second question. It checks this method; it does not establish a grade level.
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