Statistical data of breakdowns of computer XXX show that the duration for trouble-free operation of the machine can be described as a gamma distribution with a mean of 40 days and a standard deviation of 10 days. The computer is occasionally taken out for maintenance in order to insure operational condition at any time with a 95% probability.
1. How often should the computer be scheduled for maintenance? Should it be shorter or longer than the mean of 40 days?
2. Three XXX computers were acquired at the same time by an engineering consulting firm. The computers are operating under the same environment, workload, and regular maintenance schedule. The breakdown times between the computers, however, may be assumed to be statistically independent. What is the probability that at least one of the three machines will break down within the first scheduled maintenance time?