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Marginal Probability Mass Function

I am having some trouble with one of my homework problems and I would like some help on the items below.

The joint distribution of X and Y is defined by f(x,y) = |x-y|/10 for x=1,2 and y=1,2,3,4.

**a. Find f1(x), the marginal distribution of X**

This is my work so far... f1(x)=∑|x-y|/10 from y=1 to 4

f1(x)=|x-1|/10+|x-2|/10+|x-3|/10|x-4|/10 for x=1,2

I feel like this can be simplified but because of the absolute value I am unsure how?

**b. Find f2(y), the marginal distribution of Y**

f2(y)=∑|x-y|/10 from x=1 to 2

f2(y)=|1-y|/10+|2-y|/10 = |3-2y|/10 for y=1,2,3,4 .....Is this correct?

**c. Find P(Y>X)**

I don't know where to start

**d. Find P(X+Y=4)**

I don't know where to start

**e. Find P(Y<=4-X)**

I don't know where to start

**f. Are X and Y independent of dependent? Why?**

Once I have the two equations for the marginal distribution of X & Y I will be able to determine independence because if f(x,y) = f1(x)f2(y) then it will be independent.

Thanks in advance for any help you are willing to give :)