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The length of similar components produced by a company are approximated by a normal distribution model with a mean of 8 cm and a standard deviation of 0.04 cm . Let the random variable X represent the length of one component chosen at random. Accurate to 4 decimal places, evaluate \( P(X<7.99 \) OR \( X>8.1) \) 0.0062 0.4075 0.5987 0.5925 None of the above. ** Note: Do not round any z-score.

Ask by Davison Conner. in the United States
Mar 09,2025

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Answer

The probability \( P(X < 7.99 \text{ or } X > 8.1) \) is approximately 0.4075.

Solution

1. The lengths are normally distributed with mean \( \mu = 8 \) cm and standard deviation \( \sigma = 0.04 \) cm. 2. We need to compute \[ P(X < 7.99 \text{ or } X > 8.1). \] Since these two events are mutually exclusive, we have: \[ P(X < 7.99 \text{ or } X > 8.1) = P(X < 7.99) + P(X > 8.1). \] 3. **For \( X < 7.99 \):** Compute the \( z \)-score: \[ z = \frac{7.99 - 8}{0.04} = \frac{-0.01}{0.04} = -0.25. \] Thus, \[ P(X < 7.99) = \Phi(-0.25). \] By the symmetry of the normal distribution: \[ \Phi(-0.25) = 1 - \Phi(0.25). \] Typically, \( \Phi(0.25) \approx 0.5987 \), so: \[ \Phi(-0.25) \approx 1 - 0.5987 = 0.4013. \] 4. **For \( X > 8.1 \):** Compute the \( z \)-score: \[ z = \frac{8.1 - 8}{0.04} = \frac{0.1}{0.04} = 2.5. \] Thus, \[ P(X > 8.1) = 1 - \Phi(2.5). \] Typically, \( \Phi(2.5) \approx 0.9938 \), so: \[ P(X > 8.1) \approx 1 - 0.9938 = 0.0062. \] 5. **Combine the probabilities:** \[ P(X < 7.99 \text{ or } X > 8.1) \approx 0.4013 + 0.0062 = 0.4075. \] Thus, the correct answer is \( 0.4075 \).

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The Deep Dive

To evaluate \( P(X<7.99 \) OR \( X>8.1) \), we can separately find \( P(X<7.99) \) and \( P(X>8.1) \) and then add them together. First, we compute the z-scores for both values using the formula \( z = \frac{(X - \mu)}{\sigma} \), where \( \mu = 8 \) cm and \( \sigma = 0.04 \) cm. For \( X = 7.99 \): \[ z = \frac{(7.99 - 8)}{0.04} = \frac{-0.01}{0.04} = -0.25 \] For \( X = 8.1 \): \[ z = \frac{(8.1 - 8)}{0.04} = \frac{0.1}{0.04} = 2.5 \] Next, we look up these z-scores in the standard normal distribution table. 1. For \( z = -0.25 \), the cumulative probability \( P(Z < -0.25) \) is approximately 0.4013. 2. For \( z = 2.5 \), the cumulative probability \( P(Z < 2.5) \) is approximately 0.9938. Now, we compute \( P(X < 7.99) \) and \( P(X > 8.1) \): - \( P(X < 7.99) = 0.4013 \) - \( P(X > 8.1) = 1 - P(Z < 2.5) = 1 - 0.9938 = 0.0062 \) Finally, we add these two probabilities together: \[ P(X < 7.99 \ OR \ X > 8.1) = P(X < 7.99) + P(X > 8.1) = 0.4013 + 0.0062 = 0.4075 \] Thus, the answer is **0.4075**.

Related Questions

Question 12(Mulliple Choice Warth 5 points) \[ (04.06 \mathrm{HC}) \] A researcher wants to test the claim that the proportion of juniors who watch television regularly is greater than the proportion of seniors who watch television regularly She finds that 56 of 70 randomly selected juniors and 47 of 85 randomly selected seniors report watching television regularly. Construct \( 95 \% \) confidence intervals for each population proportion. Which of the statemente gives the correct outcome of the research or's tert of the dalim? The \( 95 \% \) confidence interval for juniors is (706, 894), and the \( 95 \% \) confidence interval for seniors is ( 447,659 ). Since the intervals overlap, there is not enough evidence to say the proportion of juniors who watch television regularly may be higher than that of seniors. The \( 95 \% \) confidence interval for juniors is (721, 879), and the \( 95 \% \) confidence interval for seniors is (464, 642). Since the interval for juniors is higher than the interval for seniors, there is evidence to say the proportion of juniors who watch television regularly may be higher than that of seniors. The \( 95 \% \) confidence interval for juniors is ( 706,894 ), and the \( 95 \% \) confidence interval for seniors is ( 447,659 ). Since the interval for juniors is higher than the interval for seniors, there is evidence to say the proportion of juniors who watch television regularly may be higher than that of seniors. The \( 95 \% \) confidence interval for juniors is ( \( 721, .879 \) ), and the \( 95 \% \) confidence interval for seniors is (464, 642). Since the intervals overlap, there is not enough evidence to say the proportion of juniors who watch television regularly may be higher than that of seniors.

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