Three companies, A, B and C, make computer hard drives. The proportion of hard drives that fail within one year is 0.001 for company A, 0.002 for company B and 0.005 for company C. A computer manufacturer gets 50% of their hard drives from company A, 30% from company B and 20% from company C. The computer manufacturer installs one hard drive into each computer.
(a) What is the probability that a randomly chosen computer purchased from this manufacturer will experience a hard drive failure within one year? [4 marks]
(b) I buy a computer that does experience a hard drive failure within one year. What is the probability that the hard drive was manufactured by company C? [4 marks]
(c) The computer manufacturer sends me a replacement computer, whose hard drive also fails within one year. What is the probability that the hard drives in the original and replacement computers were manufactured by the same company? [You may assume that the computers are produced independently.]
(d) A colleague of mine buys a computer that does not experience a hard drive failure [6 marks] within one year. Calculate the probability that this hard drive was manufactured by company C. [6 marks]
