Question

Read this word problem.
On a cold February morning, Colton checked the temperature on his phone and saw that it was –3°C. When he checked again after school, the temperature had dropped 3°C. What was the temperature after school?
To solve the problem, Ellen subtracted
–3–(–3) and came up with an answer of 0°C. Is Ellen correct? Why or why not?

A. Yes, Ellen is correct.

B. No. Ellen should have added -3 + 3 because she needed to add the starting temperature and the change in temperature.

C. No. Ellen should have subtracted -3 - 3 because the temperature started at -3°C and dropped 3°C.

Answer 1

To solve the problem correctly, we need to determine what happens to the temperature when it drops.

Colton's initial temperature is –3°C. After school, the temperature drops by 3°C. When something drops in temperature, we are effectively subtracting that amount from the initial temperature.

So, the correct calculation would be:

Starting temperature: –3°C
Drop in temperature: –3°C

New temperature = Initial temperature - Drop in temperature
New temperature = –3°C - 3°C = –6°C

Now, let's evaluate Ellen's reasoning:

Ellen subtracted –3 - (–3) and came up with an answer of 0°C. This is incorrect because she misapplied the operation. She should have subtracted 3 (the amount the temperature decreased) from –3 (the initial temperature).

Thus, the correct response would be:

C. No. Ellen should have subtracted -3 - 3 because the temperature started at -3°C and dropped 3°C.