City Guilds Model Questions Vol1 2020 Engineering Question 49

A reliability system consists of three subsystems arranged in series: Subsystem A, Subsystem B and Subsystem C. Subsystem A contains two identical components in parallel, each with an availability of 0.92. Subsystem B is a single component with an availability of 0.95. Subsystem C contains three identical components in series, each currently having an availability of 0.98. (a) Compute the overall system availability. (b) If the target overall availability is 0.90, determine the minimum increase (to three decimal places) required in the availability of each component of Subsystem C (assuming all three are increased by the same amount) to meet the target, while keeping the availabilities of Subsystems A and B unchanged.