Calculate the value of Kendall's tau for the following bivariate discrete distribution with joint pdf f(x, y) = x + y 15 x = 1, 2 and y = 0, 1, 2 0, otherwise Hint: You must first calculate P{ (Y, Y)(X2 -X)> 0} where (X, Y) and (X, Y) are independent pairs of random variables that have pdf f(x, y).