n flips or Bernouli trials and the probability of any particular outcome for a coin can be calculated u... u do $n=10$ trials. The probability of success in any given trial is $p=\frac{1}{2}$. You want k=3 succ... P(E|H) \cdot P(H) } { P(E) } $$
$H$ stands for any hypothesis whose probability may be affected by n