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**adebayor** 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 $\displaystyle \left( \frac{1}{6} \right)^r > \frac{1}{2}$. Using trial and error would be best for you.

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