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If the correlation coefficient between t...

If the correlation coefficient between the random variables X and Y be negative, then which of the following statements is true or false
`E(XY)ltE(X)E(Y)`

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The correct Answer is:
To determine whether the statement \( E(XY) < E(X)E(Y) \) is true or false given that the correlation coefficient between the random variables \( X \) and \( Y \) is negative, we can follow these steps: ### Step-by-Step Solution: 1. **Understand the Correlation Coefficient**: The correlation coefficient \( r \) between two random variables \( X \) and \( Y \) is defined as: \[ r = \frac{\text{Cov}(X, Y)}{\sigma_X \sigma_Y} \] where \( \text{Cov}(X, Y) \) is the covariance between \( X \) and \( Y \), and \( \sigma_X \) and \( \sigma_Y \) are the standard deviations of \( X \) and \( Y \), respectively. 2. **Express Covariance**: The covariance can be expressed in terms of expectations: \[ \text{Cov}(X, Y) = E(XY) - E(X)E(Y) \] 3. **Substitute into the Correlation Formula**: Substituting the expression for covariance into the correlation coefficient formula gives: \[ r = \frac{E(XY) - E(X)E(Y)}{\sigma_X \sigma_Y} \] 4. **Analyze the Condition for Negative Correlation**: For the correlation coefficient \( r \) to be negative, the numerator \( E(XY) - E(X)E(Y) \) must be negative. This leads to: \[ E(XY) - E(X)E(Y) < 0 \] Rearranging this inequality gives: \[ E(XY) < E(X)E(Y) \] 5. **Conclusion**: Since we have established that \( E(XY) < E(X)E(Y) \) when the correlation coefficient \( r \) is negative, we can conclude that the statement \( E(XY) < E(X)E(Y) \) is **true**. ### Final Answer: The statement \( E(XY) < E(X)E(Y) \) is **True**. ---
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