given that f(x,y) - 1/4 for (x,y)= { (0,0), (1,1),(1,-1),(2,0)} . how do i find the marginal mass functions for x and y?
I assume that minus is an equal sign.
As in the name, marginal, you sum across.
So you have 1/4 probability on these 4 points (0,0), (1,1),(1,-1),(2,0)
P(X=0)=1/4 since X is zero only once at (0,0)
P(X=1)=1/2 since X is one twice at (1,1),(1,-1)
Likewise
P(X=2)=1/4 since X is two only once at (2,0).
OK, now you do Y.