If X∼Binomial(n,p)X \sim \text{Binomial}(n, p)X∼Binomial(n,p), what is the probability generating function GX(s)=E[sX]G_X(s) = E[s^X]GX(s)=E[sX]?
(q+ps)n(q+ps)^n(q+ps)n
(p+qs)n(p+qs)^n(p+qs)n
pnsnp^n s^npnsn
nspns pnsp