If A1, A2, ..., An are the independent inputs and A is the output of a Voting gate (k-out-of-n), then the probability of the gate is:

Pr{A} = Probability of all combinations of events that events that have at least k success events.

If all events are statistically independent and identical, and the probability of each event is r, then:

Pr{A} = nCk (r)k (1-r)n-k + .... + nCn (r)n (1-r)n-n