Lucky Lumen light bulbs have an expected life that is exponentially distributed with a mean of

20,000 hours. Determine the probability that one of these light bulbs will last

a. at least 24,000 hours.

b. no longer than 4,000 hours.

c. between 4,000 hours and 24,000 hours.

15. Planetary Communications, Inc., intends to launch a satellite that will enhance reception of television programs in Alaska. According to its designers, the satellite will have an expected life of

six years. Assume the exponential distribution applies. Determine the probability that it will function for each of the following time periods:

a. More than 9 years

b. Less than 12 years

c. More than 9 years but less than 12 years

d. At least 21 years