- #1

- 118

- 0

## Homework Statement

The following table gives the joint probability mass function (p.m.f) of the random variables X and Y.

http://img170.imageshack.us/img170/555/tableph9.jpg [Broken]

Find the marginal p.m.f's [tex]P_X \left( x \right)[/tex] and [tex]P_Y \left( y \right)[/tex]

**2. The attempt at a solution**

I think I have just missed the point of this somewhere.

I know that:

[tex]{P_X \left( x \right) = \sum\limits_{all\;y} {P_{X,Y} \left( {x,y} \right)} }[/tex]

and

[tex]{P_Y \left( y \right) = \sum\limits_{all\;x} {P_{X,Y} \left( {x,y} \right)} }[/tex]

I just don't know how to apply this to the question properly.

For [tex]P_X \left( x \right)[/tex] it's the sum of [tex]{P_{X,Y} \left( {x,y} \right)}[/tex] over all y (y=0,1,2). So do we just take the first row?

i.e. 0.15+0.20+0.10 = 0.45?

Following this, would

[tex]P_Y \left( y \right)[/tex] be 0.35?

Any help would be greatly appreciated.

Cheers

Last edited by a moderator: