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December 5th, 2010, 01:48 PM  #1 
Newbie Joined: Mar 2010 Posts: 18 Thanks: 0  Joint Probability
Say for example the Probability P(AB) =1/4. The joint probability of this would be P(AB)P(B). However, you are not given the probability of B. How would you go ahead and do this?

December 5th, 2010, 04:27 PM  #2 
Global Moderator Joined: May 2007 Posts: 6,527 Thanks: 588  Re: Joint Probability
Try to state the problem precisely. I can't tell what you are looking for.

December 6th, 2010, 04:52 AM  #3 
Newbie Joined: Mar 2010 Posts: 18 Thanks: 0  Re: Joint Probability
OK. Here is the problem. The random variables X and Y are discreet distributed with the values 1,2,3,4 and 0,1,2,3. Y is B(3, 0.5)distributed. Given below is the table for the conditional probabilities P(X = iY = k) for i = 1,2,3, 4 and k = 0,1,2,3: Calculate P(X = i, Y = k) for i = 1, . . . , 4 and k = 0, . . . , 3. My understanding is that this is a joint probability. From the join probability formula, we have: P(X = i, Y = k)P(Y = k). We already have (X = i, Y = k) in the table but I don't know how I will get P(Y=K) Thanks in advance. 
December 6th, 2010, 12:57 PM  #4  
Global Moderator Joined: May 2007 Posts: 6,527 Thanks: 588  Re: Joint Probability Quote:
 
December 6th, 2010, 01:24 PM  #5 
Newbie Joined: Mar 2010 Posts: 18 Thanks: 0  Re: Joint Probability
I think it means it is binomially distributed.

December 7th, 2010, 01:00 PM  #6 
Global Moderator Joined: May 2007 Posts: 6,527 Thanks: 588  Re: Joint Probability
I'll assume it means binomial with n=3 and p=0.5. In that case P(k=0)=P(k=3)=1/8 and P(k=1)=P(k=2)=3/8.


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