- #1
Karlx
- 75
- 0
Hi everybody.
I keep on reading Rohatgi's book "An introduction to Probability and Statistics" and I have worked out the following problem:
"An urn contains r red marbles and g green marbles. A marble is drawn at random and its color noted. Then the marble drawn, together with c > 0 marbles of the same color, are returned to the urn. Suppose that n such draws are made from the urn. Prove that the probability of selecting a red marble at any draw is r/(r+g)."
I have obtained the following expression for the required probability:
[tex]
P(n) = \frac{1}{\prod_{j=0}^{n-1}(r+g+jc)} \sum_{k=0}^{n-1}(\stackrel{n-1}{k}) \prod_{j=0}^{k}(r+jc) \prod_{j=0}^{n-k-2}(g+jc)
[/tex]
This expression gives the result r/(r+g) for values n=2,3.
I have been trying to prove it for all values of n>=2, by induction, but with no success.
Perhaps anyone of you could help me.
Thanks and Happy Halloween !
I keep on reading Rohatgi's book "An introduction to Probability and Statistics" and I have worked out the following problem:
"An urn contains r red marbles and g green marbles. A marble is drawn at random and its color noted. Then the marble drawn, together with c > 0 marbles of the same color, are returned to the urn. Suppose that n such draws are made from the urn. Prove that the probability of selecting a red marble at any draw is r/(r+g)."
I have obtained the following expression for the required probability:
[tex]
P(n) = \frac{1}{\prod_{j=0}^{n-1}(r+g+jc)} \sum_{k=0}^{n-1}(\stackrel{n-1}{k}) \prod_{j=0}^{k}(r+jc) \prod_{j=0}^{n-k-2}(g+jc)
[/tex]
This expression gives the result r/(r+g) for values n=2,3.
I have been trying to prove it for all values of n>=2, by induction, but with no success.
Perhaps anyone of you could help me.
Thanks and Happy Halloween !