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2. Answer the following questions. A random variable \( X \) has a mean 8 , a variance 9 , and an unknown probability distribution. Using Chebyshev's theorem, find the lower bound of \( P(|X-8| \geq 6) \).

Ask by West Warner. in Pakistan
Jan 22,2025

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Answer

The lower bound of \( P(|X-8| \geq 6) \) is 0.25.

Solution

To find the lower bound of \( P(|X-8| \geq 6) \) using Chebyshev's theorem, we first need to understand the theorem and the given information. Chebyshev's theorem states that for any random variable \( X \) with mean \( \mu \) and variance \( \sigma^2 \), the following inequality holds: \[ P(|X - \mu| \geq k) \leq \frac{\sigma^2}{k^2} \] where \( k \) is a positive real number. Given that the mean of \( X \) is 8 and the variance is 9, we can substitute these values into the inequality: \[ P(|X - 8| \geq 6) \leq \frac{9}{6^2} \] Now, we can calculate the lower bound of \( P(|X-8| \geq 6) \) using the inequality. Calculate the value by following steps: - step0: Calculate: \(\frac{9}{6^{2}}\) - step1: Rewrite the expression: \(\frac{9}{3^{2}\times 2^{2}}\) - step2: Rewrite the expression: \(\frac{3^{2}}{3^{2}\times 2^{2}}\) - step3: Reduce the fraction: \(\frac{1}{2^{2}}\) - step4: Evaluate the power: \(\frac{1}{4}\) The lower bound of \( P(|X-8| \geq 6) \) using Chebyshev's theorem is 0.25.

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The Deep Dive

Chebyshev's theorem tells us that for any random variable, the proportion of observations that lie within \( k \) standard deviations of the mean is at least \( 1 - \frac{1}{k^2} \). In this case, the mean \( \mu = 8 \) and the variance \( \sigma^2 = 9 \), so the standard deviation \( \sigma = 3 \). To find \( P(|X - 8| \geq 6) \), we consider \( |X - 8| \geq 6 \) which is equivalent to \( |X - 8| < 6 \). Here, we define \( k \) as the number of standard deviations: \( k = \frac{6}{3} = 2 \). Now applying Chebyshev's theorem: \[ P(|X - 8| < 6) \geq 1 - \frac{1}{k^2} = 1 - \frac{1}{2^2} = 1 - \frac{1}{4} = \frac{3}{4}. \] Thus, the probability of being outside that range is: \[ P(|X - 8| \geq 6) \leq 1 - P(|X - 8| < 6) \leq 1 - \frac{3}{4} = \frac{1}{4}. \] So, the lower bound of \( P(|X - 8| \geq 6) \) is at least \( \frac{1}{4} \).

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