The temperature at 2 P. M. was 30°F. By

11 P. M. it had changed to "20°F. What

was the change in temperature?

The change in temperature was negative (-) 10 degrees.

Step-by-step explanation:

Since the temperature was 30 degrees and lowered to 20 degrees, the change was - 10 degrees.

You could solve this by taking the second temperature (in this case, 20) and subtracting 30 from it.

20 - 30 = - 10