nvm solved it Solution The answer would be 1-Probability(System does not work) When will the system not work??.. when Both A and B fail or when both D and E fail... P(Both A and B fail)=P(Both D and E fail)= 0.1*0.1 = 0.01... Hence, the answer would be 1-2*0.01 i.e. 0.98.... You got the correct answer... :).