A random variable $Y$ follows a negative binomial distribution with the number of successes $r$ and the

probability of success $p$ in each trial. What is the variance of $Y?$

A$.rp(1-p)$

B$.\frac{r}{p(1-p)}$

C$.\frac{rp}{(1-p{)}^2}$

D$.\frac{r(1-p)}{p^2}$

A diagnostic test for a disease has a probability of $0\mathrm{.}95$ of giving a positive result when the disease is present,

and a probability of $0\mathrm{.}02$ of giving a positive result when the disease is not present. If $1\%$ of the population

has the disease, what is the probability that a person has the disease given that they tested positive?

A$.0\mathrm{.}0200$

B$.0\mathrm{.}3247$

C$.0\mathrm{.}0100$

D$.0\mathrm{.}9500$