Answer:
We can prove it using the mean value theorem, as explained below.
Explanation:
Let's call f(t) the temperature of the core at the time t. So, in beginning, t= 0, f(0) = 1030ºF, and after 7 hours, f(7) = 330ºF.
The rate of decreasing can be calculated applying the MVT (Mean Value Theorem), and it would be the temeperature at 7 hours minus the temperature at t = 0 divided by 7 (which is the time interval), so:
r = (330 - 1030)/7
r = -700/7
r = -100ºF per hour