A manufacturer of light-emitting diode (LED) lights has tested its lights and found that the percent chance P that a light will fail after t hrs of use can be approximated by the following.
P = 100(1/2)^t/30,000

(a)
What is the percent chance that one of the company's LED lights will fail after 20,000 hrs? Round to the nearest tenth.


(b)
In how many hours will the chance of an LED light failing reach 40%? Round to the nearest thousand.