Consider the series-parallel networks depicted below. Each system comprises four components. The time-to-failure for components (1) and (2) is exponentially distributed with a mean of one year; the time-to-failure for components (3) and (4) is exponentially distributed with a mean of two years. All failures are assumed to be statistically independent.
Estimate the mean and standard deviation of the time-to-failure for Network A, the time-to-failure for Network B.