A computerized airline reservation system has a main computer on-line and a secondary standby computer. The on-line computer fails at a constant rate of 0.001 failure/hr, and the standby unit fails when on-line at the constant rate of 0.005 failure per hour. Assuming a 0.005 probability of a switching failure. There are no failures while the unit is in the standby mode.

(a) Determine the system reliability over a 72-hr period.

(b) The airline desires to have a system MTTF of 2000 hr. Determine the (minimum) MTTF of the main computer to achieve this goal assuming that the standby computer MTTF does not change.