Suppose that the space shuttle has three separate computer control systems: the main system and two backup duplicates of it$.$ The first backup would monitor the main system and kick in if the main system failed. Similarly, the second backup would monitor the first. We can assume that a failure of one system is independent of a failure of another system, since the systems are separate. The probability of failure for any one system on any one mission is known to be $0\mathrm{.}01.$