For a Bernoulli random variable with success probability $p$, how does one compute the probability of having a ''success'' at the $k$-th trial out of $N$ repeated and independent trials where $k \le N$ ?
1 Answer
As described in more general case here, it follows geometric distribution. You have $k$ independent trials with the same probability of success $p$, so you expect $k-1$ failures and then a success, what translates to
$$ \underbrace{(1-p)\times(1-p)\times\dots\times(1-p)}_{k-1 ~ \text{failures}} \times \underbrace{p}_{\text{success}} = (1-p)^{k-1}p $$