STAT 330 Assignment 2
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STAT 330 Assignment 2
1. Suppose the joint p.d.f of (X, Y) is f (x, y) = 4x if 0 < y < x2 , 0 < x < 1 and
0 elsewhere.
[3] (a) Find P (X ≤ 0.5, Y ≤ 0.5).
[6] (b) Find the marginal p.d.f of X and Y , respectively.
[3] (c) Find E(Y).
[5] (d) Find the conditional pdf of X given by Y = y, which is denoted by f1 (x|y).
2. Suppose X ~ Binomial(1, 0.4) and Y ~ Binomial(2, 0.4), respectively. Addi- tionally, we assume P (X = 1, Y = 2) = 0 and X and Y are uncorrelated.
[5] (a) Find the joint probability function of X and Y . (You may write it as a table.)
[3] (b) Find P (X ≤ Y).
[2] (c) Is X independent of Y? Justify your reasoning.
3. Suppose that Y = Xi , where Xi ’s are i.i.d Gamma(α, β) and N ~ Poisson(µ). We further assume that N is independent of Xi ’s.
[5] (a) Find E(Y).
[5] (b) Find the moment generation of Y .
[5] (c) Find the correlation coefficient of N and Y .
4. Suppose that X ~ Gamma(α1 , β) and Y ~ Gamma(α2 , β). In addition, X and Y are independent of each other.
[3] (a) Find E[(X 一 Y)2].
[5] (b) Find the distribution of X + Y .
[5] (c) Find E[X/(X + Y)].
5. Suppose that (X1 , X2 ) follows a BVN(µ, Σ), where µ = (µ1 , µ2 )T and Σ = ╱2σρσ2 ρσ2σ2 、
with |ρ| < 1. Let = (X1 + X2 )/2 and S2 = (X1 一 )2 + (X2 一 )2 .
[3] (a) Find the distribution of X1 + X2 .
[5] (b) Prove that X1 + X2 is independent of X1 一 X2 .
[3] (c) Is independent of S2 ? Justify your reasoning.
2023-03-07