Probability of an event

Using built-in statistical functions (Discrete Univariate Distributions).

sampleBernoulli[p_, n_] := RandomVariate[BernoulliDistribution[p], n]

Then

sampleBernoulli[.7, 10]
(* {1, 0, 1, 0, 0, 0, 1, 1, 1, 1} *)

Hope this helps.

Clear[prob]

prob[p_, n : _Integer : 1] := RandomChoice[{p, 1 - p} -> {1, 0}, n]

Total[prob[0.21321312444, 10^5]]/10.^5.

(*  0.21322  *)