City Guilds Model Questions Vol1 2025 Information Technology Question 32

An organization's security architecture consists of three independent layers: a firewall, an intrusion‑detection system (IDS), and an authentication mechanism. The probabilities that a single external attack bypasses the firewall, the IDS, and the authentication layer are respectively \(0.30\), \(0.30\) and \(0.10\). (a) For 100 independent attacks, what is the expected number of attacks that succeed in breaching all three layers? (b) Management wants the overall breach probability to be at most \(0.005\). They can improve exactly one layer by reducing its bypass probability by an absolute amount of \(0.05\). Which layer should be upgraded to meet the target, and what will be the new expected number of successful attacks after the upgrade?