The temperature at 7pm was - 5°F. The temperature began changing at the rate of - 2.5°F per hour. What was the temperature at 10pm?

AT 10 PM the temperature is: - 12.5°F

Step-by-step explanation:

Notice that from 7PM to 10 PM, there are 3 hours difference.

At 7 PM the temperature was - 5° F, then one hour later, (at 8PM it was - 2.5°F less, that is: - 7.5°F.

One hour later (9PM) : - 7.5°F - 2.5°F = - 10°F

Another hour later (10PM) : - 10°F - 2.5°F = - 12.5°F

The problem could also be solved in one step by multiplying the rate of change times "3" (due to the 3 hours elapsed between 7PM and 10PM), and using it to modify the starting value (-5°F):

At 10 PM: - 5°F + 3 * (-2.5°F) = - 5°F - 7.5°F = - 12.5°F

-12.5 degrees

Step-by-step explanation:

We start at - 5 pm

from 7pm to 10 pm is 3 hours

it drops 2.5 degrees per hour

-2.5 * 3 = - 7.5 degrees

-5 + - 7.5 = - 12.5

The temperature at 10 pm is - 12.5 degrees