Math Problem Statement

solve part e using the formula from part b

Solve part e using the formula from part b

Solution

In part e, you're asked to find the correlation between XX and YY, and compare the result to the finding from part b.

Formula for Correlation:

The correlation between XX and YY, denoted as ρ(X,Y)\rho(X, Y), is given by: ρ(X,Y)=Cov(X,Y)σXσY\rho(X, Y) = \frac{\text{Cov}(X, Y)}{\sigma_X \sigma_Y} where:

  • Cov(X,Y)\text{Cov}(X, Y) is the covariance between XX and YY,
  • σX\sigma_X is the standard deviation of XX,
  • σY\sigma_Y is the standard deviation of YY.

Steps to Compute Correlation:

  1. Covariance Cov(X,Y)\text{Cov}(X, Y):
    The covariance is calculated using: [ \text{Cov}(X, Y) = E[XY] - E[X]E[Y] ] From part b, you are given a formula for E(XrYs)E(X^r Y^s). You can use this formula to find E[XY]E[XY] by setting r=1r = 1 and s=1s = 1.

  2. Means E[X]E[X] and E[Y]E[Y]:
    These are typically computed by integrating the marginal PDFs fX(x)f_X(x) and fY(y)f_Y(y), which you may have found in part c.

  3. Standard Deviations σX\sigma_X and σY\sigma_Y:
    Use the variance formulas: [ \sigma_X = \sqrt{E[X^2] - (E[X])^2} ] [ \sigma_Y = \sqrt{E[Y^2] - (E[Y])^2} ]

Once you have E[XY]E[XY], E[X]E[X], E[Y]E[Y], σX\sigma_X, and σY\sigma_Y, you can substitute into the correlation formula to find ρ(X,Y)\rho(X, Y).


Do you want me to compute specific values or clarify anything? Here are 5 possible questions that relate to this problem:

  1. What is the formula for the marginal PDFs of XX and YY?
  2. How do we compute E[X]E[X] and E[Y]E[Y] using marginal PDFs?
  3. How is E(XY)E(XY) computed directly from the joint PDF?
  4. What is the physical interpretation of correlation in this context?
  5. How does the independence of XX and YY affect the correlation?

Tip: If XX and YY are independent, their correlation will be zero. Always check independence to simplify the computation.

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Math Problem Analysis

Mathematical Concepts

Probability Density Functions
Covariance
Correlation
Expected Values
Marginal Distributions

Formulas

Cov(X, Y) = E[XY] - E[X]E[Y]
σ_X = √(E[X^2] - (E[X])^2)
σ_Y = √(E[Y^2] - (E[Y])^2)
ρ(X, Y) = Cov(X, Y) / (σ_X * σ_Y)

Theorems

Law of Total Expectation
Independence of Random Variables

Suitable Grade Level

University Level - Probability and Statistics