The HP dvd1040i 20X Multi format DVD Writer has an MTBF of 70,000 hours. (a) Assuming continuous

Question:

The HP dvd1040i 20X Multi format DVD Writer has an MTBF of 70,000 hours.
(a) Assuming continuous operation, what is the probability that the DVD writer will last more than 100,000 hours?
(b) Less than 50,000 hours?
(c) At least 50,000 hours but not more than 80,000 hours? (Product specifications are from www.hp.com.)