1. ## binomial

let x be a random variable that follows a binomial distribution with parameters n=20 and p=2/3 (i.e.X~Bin (20,2/3)

What is the probability that X takes the value 13?

Compute the exception, E(X), and variance, var(X), of X

Also another question giving me trouble is:

A die is rolled successively until a 6 comes up. How many rolls are necessary before the probability is at least 1/2 that the 6 will turn up at least once? What probability definition are you using? Indicate what probability rules you are using (if any).

WOULD BE REALLY GRATEFUL IF SOMEONE COULD POST THE ANSWERS TO THESE QUESTIONS!!!!

2. remember that $E[X] = np$ and $\sigma_{X} = \sqrt{npq}$.

let x be a random variable that follows a binomial distribution with parameters n=20 and p=2/3 (i.e.X~Bin (20,2/3)

What is the probability that X takes the value 13?

Compute the exception, E(X), and variance, var(X), of X

Mr F says: This question is an application of the basic formulae. Where exactly are you stuck?

Also another question giving me trouble is:

A die is rolled successively until a 6 comes up. How many rolls are necessary before the probability is at least 1/2 that the 6 will turn up at least once? What probability definition are you using? Indicate what probability rules you are using (if any).

Mr F says: Find the smallest integer value of r that solves $\left( \frac{1}{6} \right)^r > \frac{1}{2}$. Using trial and error would be best for you.

WOULD BE REALLY GRATEFUL IF SOMEONE COULD POST THE ANSWERS TO THESE QUESTIONS!!!!
..