Bismuth has a half-life period of $5 \text{ days}$. $A$ sample originally has a mass of $1000 \text{ mg}$. What is the mass of Bismuth remaining after $30 \text{ days}$ (in $.625$)?

Mean and variance of a binomial probability distribution are $4$ and $\frac{4}{3}$ respectively. Then the probability of at least two successes is equal to:

If the mean and variance of a binomial variate $X$ are $8$ and $4$ respectively,then $P(X < 3)$ equals to

Let $X \sim B(n, p)$ with mean $\mu$ and variance $\sigma^2$. If $\mu=2 \sigma^2$ and $\mu+\sigma^2=3$,then $P(X \leq 3)=$

$A$ shooter can hit a given target with probability $\frac{1}{4}$. She keeps firing a bullet at the target until she hits it successfully three times and then she stops firing. The probability that she fires exactly six bullets lies in the interval

Six balls are drawn successively from an urn containing $7$ red and $9$ black balls. Determine whether or not the trials of drawing balls are Bernoulli trials when the ball drawn is not replaced in the urn after each draw.