The temperature of a certain cup of coffee 6 minutes after it was poured was 120 degrees Fahrenheit. If the temperature F of the coffee t minutes after it was poured can be determined by the formula F = 120*2^(-at) + 60, where F is in degrees Fahrenheit and a is a constant. Then the temperature of the coffee 30 minutes after it was poured was how many degrees Fahrenheit? Choose the correct choice from the following answers.
A) 65
B) 63.75
C) 80
D) 85
E) 90
First, we have to find a.   We know that after t=6 minutes the temperature F=120 degrees.   Hence:   120 = 120*(2^-6a)+60   60 = 120*(2^-6a)   60/120 = 2^-6a   1/2 = 2^-6a   2^-1 = 2^-6a   -1 = -6a   1/6 = a   Now we need to find F after t=30 minutes:   F = 120*(2^-1/6*30)+60   F = 120* (2^-5) +60   F = 120* (1/2^5) +60   F = 120*1/32 +60   F = 3.75+60= 
<gadget id="calculator">3.75+60</gadget>
<output>63.75</output>
63.75   Answer 63.75!
<result>B</result>
The temperature of a certain cup of coffee 6 minutes after it was poured was 120 degrees Fahrenheit. If the temperature F of the coffee t minutes after it was poured can be determined by the formula F = 120*2^(-at) + 60, where F is in degrees Fahrenheit and a is a constant. Then the temperature of the coffee 30 minutes after it was poured was how many degrees Fahrenheit?