# Probability Distributions Problem

• March 18th 2009, 05:20 PM
VGDude85
Probability Distributions Problem
I am trying to do this problem and I have the answer key of course to it. But I can't quite figure out how to get there if someone could help me out.

An urn holds 5 white and 3 black marbles. If 2 marbles are to be drawn at random with replacement and X denotes the number of white marbles, find the probability distribution for X.

Thanks for any help.
• March 18th 2009, 05:38 PM
matheagle
that's a binomial n=2, p=5/8
(if you do it this without replacement it's a hypergeometric)

$P(X=x)={2 \choose x}(5/8)^x(3/8)^{2-x}$, x=0,1,2.
• March 18th 2009, 05:59 PM
VGDude85
Was that the binomial distribution?
• March 18th 2009, 06:03 PM
matheagle
that is binomial, since the probability of succes (white) remains at 5/8
and the probability of failure stays at 3/8.

If you do not replace these marbles, then it will be a hypergeometric rv.
• March 18th 2009, 06:06 PM
VGDude85
Oh ok, I see that now thank you :)