Prob and Stat Homework 8
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Prob and Stat
Homework 8
Problem 1
Suppose the distribution of Y , conditional on X = x, is N (x, x2 ) and that the marginal distribution of X is uniform(0,1).
(1) Find E(Y), var(Y), and cov(X, Y).
(2) Prove that Y/X and X are independent.
Problem 2
Let X1 , X2 and X3 be uncorrelated random variables, each with mean µ and variance σ2 . Find, in terms of µ and σ2 , cov(X1 + X2 , X2 + X3 ) and cov(X1 + X2 , X1 - X2 )
Problem 3
The random pair (X, Y) has the joint distribution as below:
P (X = 1, Y = 2) = 1/12, P (X = 1, Y = 3) = 1/6, P (X = 2, Y = 2) = 1/6, P (X = 2, Y = 4) = 1/3, P (X = 3, Y = 2) = 1/12, P (X = 3, Y = 3) = 1/6.
(1) Find the conditional probability mass function fX[Y (x|y) and verify that X and Y are dependent.
(2) Give a probability table for random variables U and V that have the same marginals as X and Y but are independent.
Problem 4
Let X1 , X2 and X3 be independent normally distributed with mean -1 and variance 2. Define U = X1 - X2 and V = X2 + X3 .
(1) Calculate the covariance between X1 - X2 and X2 + X3 .
(2) If we further assume that Xi ’s are normally distributed, what is the joint distribution for (U, V)?
2021-12-25