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The random variables X and Y have the joint PMF: px,y(x, y)=c*(x+y)^(2) if x belongs to {1,2,4} and y belongs to {1,3} and otherwise px,y(x,y) =0. Find the value of c. Find P(Y<X) and P(Y=X).

Question

The random variables X and Y have the joint PMF: px,y(x, y)=c*(x+y)^(2) if x belongs to {1,2,4} and y belongs to {1,3} and otherwise px,y(x,y) =0. Find the value of c. Find P(Y<X) and P(Y=X).

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Solution

To find the value of c, we need to use the fact that the sum of all probabilities in a probability mass function (PMF) must equal 1.

The possible pairs (x, y) are (1,1), (1,3), (2,1), (2,3), (4,1), (4,3). We sum the probabilities for all these pairs and set it equal to 1:

c * [(1+1)^2 + (1+3)^2 + (2+1)^2 + (2+3)^2 + (4+1)^2 + (4+3)^2] = 1 c * [4 + 16 + 9 + 25 + 25 + 49] = 1 c * 128 = 1

So, c = 1/128.

Next, to find P(Y<X) and P(Y=X), we need to sum the probabilities for the pairs where Y<X and Y=X, respectively.

For P(Y<X), the pairs are (2,1), (4,1), (4,3). So, P(Y<X) = c * [(2+1)^2 + (4+1)^2 + (4+3)^2] = 1/128 * [9 + 25 + 49] = 83/128.

For P(Y=X), the pairs are (1,1). So, P(Y=X) = c * (1+1)^2 = 1/128 * 4 = 1/32.

This problem has been solved

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