The temperature of a certain cup of coffee 30 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?
Choices.
A) 65	B) 120	C) 80	D) 85	E) 90
First, we have to find a.   We know that after t=30 minutes the temperature F=120 degrees.   Hence:   120 = 120*(2^-30a)+60   60 = 120*(2^-30a)   60/120 = 2^-30a   1/2 = 2^-30a   2^-1 = 2^-30a   -1 = -30a   1/30 = a   Now we need to find F after t=30 minutes:   F = 120*(2^-1/30*30)+60   F = 120* (2^-1) +60   F = 120* (1/2^1) +60   F = 120*1/2 +60   F = 60+60= 
<gadget id="calculator">60+60</gadget>
<output>120</output>
120   Answer 120!
<result>B</result>
The temperature of a certain cup of coffee 30 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?