A satellite has an initial radioisotope power supply of 65 watts (W). The power output in watts is given by
Where t is the time in days. Solve for t to find the time when the power supply is 26 W.

A) 243 days
B) 250 days
C) 99 days
D) 229 days
E) 222 days

Question

A satellite has an initial radioisotope power supply of 65 watts (W). The power output in watts is given by ​  ​
Where t is the time in days. Solve for t to find the time when the power supply is 26 W.
​
A) 243 days 
B) 250 days 
C) 99 days 
D) 229 days 
E) 222 days

Quizplus · Accepted Answer

We need to solve the equation: 
11eac9cf_f8e3_4b4a_a07b_0765738ab42b_TB7816_11 = 26
Taking natural logarithm on both sides, 
ln(11eac9cf_f8e3_4b4a_a07b_0765738ab42b_TB7816_11) = ln(26) 
ln(11) + t/240 = ln(26) 
t/240 = ln(26) - ln(11) 
t/240 = ln(26/11) 
t = 240 ln(26/11) 
t ≈ 228.81

Rounding up to the nearest day, t ≈ 229. Therefore, after about 229 days, the power output of the satellite will be 26 W. So the best choice is D).

A Satellite Has an Initial Radioisotope Power Supply of 65