word problem

Question

Nuclear energy derived from radioactive isotopes can be used to supply power to space vehicles. The output of the power supply for a power plant is given by the function defined by y = 80e^-0.00125t, where y is measured in watts and t is the time in days. After how many days will the output be reduced to 50 watts?

Answer 1

Power is given by

y =80 e ^-0.00125

 Y becomes 50 watts 

So

50 = 80 e ^-0.00125

80/50 = e ^0.00125 

8/5 = 1.6 = e ^0.00125

ln 1.6 = 0.00125 *t

t =ln1.6/0.00125 = 376 days