Hi Harish21,

I wonder if I might bounce another one off you. This time it's three variables, summing one out. It should be similar to the previous one, but again I must be being even dumber than usual.

It is:

Given the joint:

Where

and

Find the joint marginal

Which, I think, is:

with the same conditions as above, right?

I did the same trick you did before with the factor I think

so,

Which gives the right factor for a joint multinomial for x and y, n=3,

and

i.e.

Which is what the sum over z should reduce to, right?

But, damn it, I can't seem to massage out this distribution from the sum over z in a similar way to before.

Thanks in advance for any help. BW, MD