OR Gate
If A1, A2, ..., An are the inputs and A is the output of an OR gate, then the probability of (occurrence of the output of) the gate is:
Pr{A}=Pr{A1}+Pr{A2\~A1}+....+Pr{An\~A1,~A2,....,~An–1}
If all events are independent, then:
Example
Events A and B are independent and are connected to an OR gate. Given that the probabilities of these events are 0.1 and 0.2 respectively, then the gate probability is:
1–(1–0.1)(1–0.2)=0.28