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Joint Probability Distributions

Carla1985

Member
Feb 14, 2013
93
I have this question:

Screen Shot 2013-03-11 at 11.40.06 copy.jpg


and I'm a little confused. To calculate joint distributions in the earlier questions i was using:


[TEX]P_{(\xi1,\xi2)}(x1,x2)=P_{(\xi1)}(x1)P_{(\xi2)}(x2)[/TEX]


But that would mean that if:


[TEX]P_{(\xi1,\xi2)}(2,0)=0\ either\ P_{(\xi1)}(2)=0\ or\ P_{(\xi2)}(0)=0[/TEX]


which cant be true in either case as


[TEX]P_{(\xi1,\xi2)}(1,0)\ isnt\ 0\ and\ neither\ is\ P_{(\xi1,\xi2)}(2,1)[/TEX]


Can someone please explain what I'm missing. Thanks :/
 

Carla1985

Member
Feb 14, 2013
93
Nevermind, I found my mistake. This was only for independent variables, which these obviously aren't :)