Derivative at a point word problem

Question

precal · Answer

After being poured into a cup, coffee cools so that its temperature T(t) is represented by the function$$T(t)=70+110e ^{^{-t/2}}$$

precal · Answer

where t is measured in mins and T(t) is measured in degrees Fahrenheit.

precal · Answer

1) What is the temperature of the coffee 5 mins after it has been poured into the cup?
2) Is the temperature decreasing faster 1 minute after it is poured or 3 minutes after it is poured?  Give a reason for your answer.

precal · Answer

Question 1 I just did T(5) and got 79.029 degrees Fahrenheit
Question 2 I did T ' (1)  and got -33.36 and T'(3) and got -12.27 but not sure I did these correctly.  I got stuck on the reason for my answer.

anonymous · Answer

33.36> 12.27 --> the rate at 1degree is bigger than it is at 3 degree. 
the minus sign in the front shows the tangent line direction from left to right \, not from right to left like /. They don't mean -33.36 < -12.27