Calc
posted by Erica .
A body of an unknown temperature was placed in a room that was held at 30°F. After 10 minutes, the body's temperature was 0°F, and 20 minutes after the body was placed in the room the body's temperature was 15°F. Estimate the body's initial temperature.
Thank you!!

I am going to assume that the heat flow into the body is proportional to the difference between body temp T and 30 and rate of change of T is proportional to heat flow .
dT/dt = k (30T)
try T = ae^kt + 30
that is 30 at t>oo and 30a at t = 0
so
0 = a e^10k + 30
15= a e^20k + 30
30 = a e^10k
45 = a e^20 k
a = 30/e^10k
45 = 30 (e^20k/e^10k)
45/30 = e^10k
I think you can take it from there, check arithmetic 
the 8th line is the simplification of the sixth line,,, im wandering why it is 45? is the algebraic solution wrong?