Question: Sum not working as intended.

I'm working with some sum values, but for some reason that I can't figure out, this sum always returns 1.
Have I made some mistake in the way it's supposed to be typed in or why does it return 1? Below the sum I've filled out the spots manually to show how I want them to be.


 

``

x := 2; y := 2; sum(binomial(y, i)*(1/3)^i*(2/3)^(y-i)*(sum(binomial(x, j)*(1/3)^j*(2/3)^(x-j), j = i+1 .. x)), i = 0 .. y)

1

(1)

binomial(y, 0)*(1/3)^0*(2/3)^(y+0)*(sum(binomial(x, j)*(1/3)^j*(2/3)^(x-j), j = 1 .. x))+(1/3)*binomial(y, 1)*(2/3)^(y-1)*(sum(binomial(x, j)*(1/3)^j*(2/3)^(x-j), j = 2 .. x))+binomial(y, 2)*(1/3)^2*(2/3)^(y-2)*(sum(binomial(x, j)*(1/3)^j*(2/3)^(x-j), j = 3 .. x))

8/27

(2)

``


 

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