first off we regroup things so that we have 5 Republicans and 8 non-Republicans
this gets us
\(P[R]=\dfrac{5}{13},~P[!R] = \dfrac{8}{13}\)
now we have a simple Binomial distribution with parameters \(n=3,~p=\dfrac{5}{13}\)
\(P[3] = \left(\dfrac{5}{13}\right)^3 = \dfrac{125}{2197}\)
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