# conditional probability

• Apr 15th 2007, 07:54 AM
conditional probability
Hi,
I would like some help with this problem

If X1 and X2 are two discrete random variables with joint probability distribution given by the following bivariate table.(table attached)

1- Find the probability distributuon of X1

here I did:
P(X=0)=0.05+0.15+0.05=0.25
P(X=1)=0.04+0.1+0.06=0.20
P(X=2)=...
P(X=3)=...
.

2-Find the conditional probability distribution of X2 given X1=2.
here I did:
P(X2|2)=0.08+0.05+0.15
But I am not sure.

thank you
• Apr 15th 2007, 09:11 AM
CaptainBlack
Quote:

Hi,
I would like some help with this problem

If X1 and X2 are two discrete random variables with joint probability distribution given by the following bivariate table.(table attached)

1- Find the probability distributuon of X1
here I did:
P(X=0)=0.05+0.15+0.05=0.25
P(X=1)=0.04+0.1+0.06=0.20
P(X=2)=...
P(X=3)=...

This is OK just complete the calculation of the marginal distribution

Quote:

2-Find the conditional probability distribution of X2 given X1=2.
here I did:
P(X2|2)=0.08+0.05+0.15
But I am not sure.

thank you
P(X2=0|X1=2) = 0.08/P(X1=2) = 0.08/0.28 = 0.286
P(X2=1|X1=2) = 0.05/P(X1=2) = 0.05/0.28 = 0.179
P(X2=2|X1=2) = 0.15/P(X1=2) = 0.15/0.28 = 0.536

RonL