The number of injections using a needle contaminated with the AIDS virus that is required to detect an
exposure to the virus is denoted here as the random variable X, and it follows the following probability
distribution:


a. Find the expected number of injections required for detectable exposure of the virus, E(X).

b. Find the variance of the random variable X.

c. Let X and Y denote the number of injections using AIDS contaminated needles for each of two
people, respectively, where X and Y both follow the distribution above. Further, assume that X
and Y are statistically independent. What is the probability that both exhibit a detectable exposure
after only one injection?

will be donating the rest of my fg for whoever is kind enough to take the time to help me out

This post was edited by Si7c on Feb 28 2014 03:35pm

a) All you have to do is compute the expected value E(X) which is 1 * 0.45 + 2 * 0.35 + 3 * 0.1 etc... , see http://en.wikipedia.org/wiki/Expectedvalue for a full explaination
b ) You must compute the variance, see http://en.wikipedia.org/wiki/Variance , basically V(X) = E(X^2) - E(X)^2 = (1 * 0.45 + 4 * 0.35 + 9 * 0.1 etc...) - E(X)^2 that you computed above
c) Assuming X=1 and Y=1 are independant events then P(X=1 AND Y=1) = P(X=1)P(Y=1) = 0.45^2 (have others confirm this tho)

This post was edited by m0hawk on Feb 28 2014 04:24pm

thank you very much; donated as promised.. saved me a lot of trouble!

This post was edited by Si7c on Feb 28 2014 04:22pm

stats...

it will only get worse

godspeed!