Why are there two different versions of the mean and variance for negative binomial distributions

Why are there two different versions of the mean and variance for negative

binomial distributions



On a wiki proof site, I've seen these formulas used for the mean and

variance:

$E[X] = \frac{rp}{1-p}$ and $Var[X] = \frac{rp}{(1-p)^2}$. Yet on the Penn

State site, they have these two different formulas: $E[X] = \frac{r}{p}$

and $Var[X] = \frac{r(1-p)}{p^2}$.