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Question 3 of 7 (s points) I Question Attempt 1 of 5 \( \checkmark 1 \) \( \checkmark 2 \) 3 4 5 6 7 Use the normal approximation to the binomial to find the probability for \( n=53, p=0.9 \), and \( X \leq 40 \). Use The Standard Normal Distribution Table. Round \( z \) value calculations to 2 decimal places and final answer to at least 4 decimal places. The probability is \( \square \) .

Ask by Hampton Sullivan. in the United States
Mar 11,2025

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The probability is approximately 0.0005.

Solution

Let \( X \) be a binomial random variable with parameters \( n = 53 \) and \( p = 0.9 \). We wish to estimate \[ P(X \leq 40) \] using the normal approximation. 1. Compute the mean and variance of \( X \): \[ \mu = np = 53 \times 0.9 = 47.7, \] \[ \sigma^2 = np(1-p) = 53 \times 0.9 \times 0.1 = 4.77. \] Thus, the standard deviation is \[ \sigma = \sqrt{4.77} \approx 2.19. \] 2. Apply the continuity correction. We estimate \[ P(X \leq 40) \approx P(Y \leq 40.5), \] where \( Y \) is normally distributed with mean \( 47.7 \) and standard deviation \( 2.19 \). 3. Compute the \( z \)-score for \( Y = 40.5 \): \[ z = \frac{40.5 - 47.7}{2.19} \approx \frac{-7.2}{2.19} \approx -3.29. \] (Rounding to two decimal places, we have \( z \approx -3.29 \).) 4. Use the standard normal table to find \( P(Z \leq -3.29) \). From the table, \[ P(Z \leq -3.29) \approx 0.0005. \] Thus, the probability is \[ \boxed{0.0005}. \]

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To use the normal approximation for a binomial distribution, we first need to calculate the mean \(\mu\) and the standard deviation \(\sigma\). For a binomial distribution, \(\mu = n \cdot p = 53 \cdot 0.9 = 47.7\) and \(\sigma = \sqrt{n \cdot p \cdot (1-p)} = \sqrt{53 \cdot 0.9 \cdot 0.1} \approx 2.74\). Next, we convert \(X \leq 40\) to a z-score: \(z = \frac{X - \mu}{\sigma} = \frac{40 - 47.7}{2.74} \approx -2.80\). Looking up this z-value in the standard normal distribution table, we find that the cumulative probability is approximately \(0.0026\). So, the probability \(P(X \leq 40)\) is roughly equal to \(0.0026\) when rounded to four decimal places. Therefore, the probability is \(0.0026\).

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