An Instructor has given a short quiz consisting of two parts. For a randomly selected student let X = the number of points earned on the 1st part of the quiz and let Y = the number of points earned on the 2nd part. Suppose that the joint pmf of X and Y is given in the following table: _px(x,y) a. b. C. d. 0 X 5 10 0 0.02 0.04 0.01 Y 5 0.06 0.15 0.15 10 0.02 0.2 0.14 15 0.1 0.1 0.01 If the score recorded in the gradebook is the total number of points earned on the two parts, what is the expected recorded score E[X + Y]? Compute the covariance between X and Y. Compute the correlation coefficient, Pxy, for this X and Y. Does it appear that there is an association between the number of points earned on the two parts of this quiz? Explain your reasoning.

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### Quiz Analysis using Joint PMF

#### Introduction
An instructor has given a short quiz consisting of two parts. For a randomly selected student, let \( X \) represent the number of points earned on the 1st part of the quiz and \( Y \) represent the number of points earned on the 2nd part. The joint probability mass function (pmf) of \( X \) and \( Y \) is provided in the following table:

#### Joint PMF Table
\[ p_{XY}(x, y) \]

| \( X \backslash Y \) | 0    | 5    | 10    | 15   |
|---|------|------|------|------|
| 0 | 0.02 | 0.06 | 0.02 | 0.1  |
| 5 | 0.04 | 0.15 | 0.2  | 0.1  |
| 10| 0.01 | 0.15 | 0.14 | 0.01 |

### Questions and Solutions

a. **Expected Total Recorded Score \( E[X + Y] \):**
   - Compute the expected value of \( X + Y \) by calculating \( E[X] \) and \( E[Y] \), then summing them up.
   
b. **Covariance Between \( X \) and \( Y \):**
   - Compute the covariance to understand how \( X \) and \( Y \) vary together.
   
c. **Correlation Coefficient \( \rho_{XY} \):**
   - Calculate the correlation coefficient to measure the strength and direction of the linear relationship between \( X \) and \( Y \).

d. **Association Between \( X \) and \( Y \):**
   - Analyze whether there is an association between the number of points earned on the two parts of the quiz and explain the reasoning. 

### Detailed Steps for Solution:

**1. Expected Value of X and Y:**
   \[
   E[X] = \sum_{x} x \times P(X=x) 
   \]
   Calculate the marginal probability for \( X \) and \( Y \) and compute their expected values.
   
**2. Expected Value of X + Y:**
   \[
   E[X+Y] = E[X] + E[Y]
   \]
   
**3. Computing Covariance \(
Transcribed Image Text:### Quiz Analysis using Joint PMF #### Introduction An instructor has given a short quiz consisting of two parts. For a randomly selected student, let \( X \) represent the number of points earned on the 1st part of the quiz and \( Y \) represent the number of points earned on the 2nd part. The joint probability mass function (pmf) of \( X \) and \( Y \) is provided in the following table: #### Joint PMF Table \[ p_{XY}(x, y) \] | \( X \backslash Y \) | 0 | 5 | 10 | 15 | |---|------|------|------|------| | 0 | 0.02 | 0.06 | 0.02 | 0.1 | | 5 | 0.04 | 0.15 | 0.2 | 0.1 | | 10| 0.01 | 0.15 | 0.14 | 0.01 | ### Questions and Solutions a. **Expected Total Recorded Score \( E[X + Y] \):** - Compute the expected value of \( X + Y \) by calculating \( E[X] \) and \( E[Y] \), then summing them up. b. **Covariance Between \( X \) and \( Y \):** - Compute the covariance to understand how \( X \) and \( Y \) vary together. c. **Correlation Coefficient \( \rho_{XY} \):** - Calculate the correlation coefficient to measure the strength and direction of the linear relationship between \( X \) and \( Y \). d. **Association Between \( X \) and \( Y \):** - Analyze whether there is an association between the number of points earned on the two parts of the quiz and explain the reasoning. ### Detailed Steps for Solution: **1. Expected Value of X and Y:** \[ E[X] = \sum_{x} x \times P(X=x) \] Calculate the marginal probability for \( X \) and \( Y \) and compute their expected values. **2. Expected Value of X + Y:** \[ E[X+Y] = E[X] + E[Y] \] **3. Computing Covariance \(
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