Math Problem Statement

The joint probability distribution table for two random variables X and Y is as follows Y X -2 -1 4 5 1 0.1 0.2 0 0.3 0.1 0.1 0 2 0.2 Determine the marginal probability distributions of X and Y. Also compute (a) Expectations of X and Y (b) Standard deviation of X and Y (c) Covariance of X and Y (d) Correlation of X and Y.

Solution

We are given a joint probability distribution table for two random variables XX and YY. Let's extract the values first to determine the marginal distributions, expectations, standard deviations, covariance, and correlation.

1. Joint Probability Distribution Table

Y / X-2-145Marginal PXP_X
10.10.200.3P(X=1)=0.6P(X = 1) = 0.6
00.10.100P(X=0)=0.2P(X = 0) = 0.2
2000.20P(X=2)=0.2P(X = 2) = 0.2

Step 1: Marginal Probability Distributions of X and Y

  • Marginal probability distribution of XX

We sum over all the values of YY for each value of XX:

P(X=1)=0.1+0.2+0+0.3=0.6P(X = 1) = 0.1 + 0.2 + 0 + 0.3 = 0.6 P(X=0)=0.1+0.1+0+0=0.2P(X = 0) = 0.1 + 0.1 + 0 + 0 = 0.2 P(X=2)=0+0+0.2+0=0.2P(X = 2) = 0 + 0 + 0.2 + 0 = 0.2

Thus, the marginal distribution of XX is:

XX102
PXP_X0.60.20.2
  • Marginal probability distribution of YY

We sum over all the values of XX for each value of YY:

P(Y=2)=0.1+0.1+0=0.2P(Y = -2) = 0.1 + 0.1 + 0 = 0.2 P(Y=1)=0.2+0.1+0=0.3P(Y = -1) = 0.2 + 0.1 + 0 = 0.3 P(Y=4)=0+0+0.2=0.2P(Y = 4) = 0 + 0 + 0.2 = 0.2 P(Y=5)=0.3+0+0=0.3P(Y = 5) = 0.3 + 0 + 0 = 0.3

Thus, the marginal distribution of YY is:

YY-2-145
PYP_Y0.20.30.20.3

Step 2: Expectations of XX and YY

  • Expectation of XX

E(X)=xxPX(x)=10.6+00.2+20.2=0.6+0.4=1E(X) = \sum_{x} x \cdot P_X(x) = 1 \cdot 0.6 + 0 \cdot 0.2 + 2 \cdot 0.2 = 0.6 + 0.4 = 1

  • Expectation of YY

E(Y)=yyPY(y)=(2)0.2+(1)0.3+40.2+50.3E(Y) = \sum_{y} y \cdot P_Y(y) = (-2) \cdot 0.2 + (-1) \cdot 0.3 + 4 \cdot 0.2 + 5 \cdot 0.3 E(Y)=0.40.3+0.8+1.5=1.6E(Y) = -0.4 - 0.3 + 0.8 + 1.5 = 1.6

Step 3: Standard Deviation of XX and YY

  • Variance of XX

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Math Problem Analysis

Mathematical Concepts

Probability Theory
Marginal Distributions
Expectation
Variance
Covariance
Correlation

Formulas

Marginal distribution of X: P(X = x) = Σ P(X = x, Y = y)
Expectation of X: E(X) = Σ x * P(X = x)
Variance of X: Var(X) = E(X^2) - [E(X)]^2
Covariance: Cov(X, Y) = E(XY) - E(X)E(Y)
Correlation: Corr(X, Y) = Cov(X, Y) / (σ_X * σ_Y)

Theorems

Law of Total Probability
Covariance and Correlation Definitions

Suitable Grade Level

Undergraduate Level (Probability and Statistics)