A system was set up in parallel with two components, A and B. The probability of failure for A is .20 and for B is .10. In order for the system to fail, both must fail. What is the probability of a system failure? Solution P( system to fail, both must fail ) = 1 - P( A Fail) * P( B Fail) = 1 - [ (1-0.20) ( 1-0.10) ] = 1 - 0.72 = 0.28.