Final answer:
The system reliability of the four components in series is 0.6561
Step-by-step explanation:
To find the system reliability, we need to calculate the reliability of the series combination of the four components A, B, C, and D. In a series configuration, the reliability is given by multiplying the individual reliabilities of the components.
Reliability of the system = Reliability of component A * Reliability of component B * Reliability of component C * Reliability of component D = 0.9 * 0.9 * 0.9 * 0.9 = 0.6561
Therefore, the system reliability is 0.6561.