this is the link for my question httptinypiccomr2mg9wm98Solu

this is the link for my question

http://tinypic.com/r/2mg9wm9/8

Solution

Given that A,B, C and D are independent.

Hence P(AB) = Prob A and B work = 0.9(0.95) = 0.855

P(CD) = Prob C and D work = (0.85)(0.8)

=0.68

Prob for AB and Cd are equally likely

P(system works) =0.5( P(AB)+P(CD))

= 0.7675