An electrical firm manufactures light bulbs that have a length of life that is approximately normally distributed with a standard deviation of 40 hours. If a sample of 30 bulbs has an average life of 780 hours, find a 96% confidence interval for the population mean of all bulbs produced by this firm.
An electrical firm manufactures light bulbs that have a length of life that is approximately normally distributed with a standard deviation of 40 hours. If a sample of 30 bulbs has an average life of 780 hours, find a 96% confidence interval for the population mean of all bulbs produced by this firm.
MATLAB: An Introduction with Applications
6th Edition
ISBN:9781119256830
Author:Amos Gilat
Publisher:Amos Gilat
Chapter1: Starting With Matlab
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![**Problem 2.**
An electrical firm manufactures light bulbs that have a length of life that is approximately normally distributed with a standard deviation of 40 hours. If a sample of 30 bulbs has an average life of 780 hours, find a 96% confidence interval for the population mean of all bulbs produced by this firm.
**Solution:**
To find a 96% confidence interval for the population mean, we use the formula for the confidence interval of the mean when the population standard deviation is known:
\[ \bar{X} \pm Z \left( \frac{\sigma}{\sqrt{n}} \right) \]
Where:
- \(\bar{X}\) is the sample mean
- \(Z\) is the Z-value from the standard normal distribution corresponding to the desired confidence level
- \(\sigma\) is the population standard deviation
- \(n\) is the sample size
Given:
- Sample mean (\(\bar{X}\)) = 780 hours
- Population standard deviation (\(\sigma\)) = 40 hours
- Sample size (\(n\)) = 30
- Confidence level = 96%
First, we need to find the Z-value for a 96% confidence level. The 96% confidence level corresponds to a Z-value of approximately 2.05 (You can find this value in standard Z-tables or using software/tools for more accuracy).
Now, we calculate the margin of error:
\[ \text{Margin of Error} = Z \left( \frac{\sigma}{\sqrt{n}} \right) = 2.05 \left( \frac{40}{\sqrt{30}} \right) \approx 14.97 \]
Next, we calculate the confidence interval:
\[ \text{Confidence Interval} = \bar{X} \pm \text{Margin of Error} \]
\[ \text{Confidence Interval} = 780 \pm 14.97 \]
Therefore, the 96% confidence interval for the population mean is:
\[ 780 - 14.97 \leq \mu \leq 780 + 14.97 \]
\[ 765.03 \leq \mu \leq 794.97 \]
So, we are 96% confident that the population mean life of all light bulbs produced by this firm is between 765.03 hours and 794.97 hours.](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2Fabd5e741-0235-409f-80de-883f5f0e5da7%2Fd71a62c5-2937-40cc-800c-ae24261499d3%2Ftrsi6lh_processed.jpeg&w=3840&q=75)
Transcribed Image Text:**Problem 2.**
An electrical firm manufactures light bulbs that have a length of life that is approximately normally distributed with a standard deviation of 40 hours. If a sample of 30 bulbs has an average life of 780 hours, find a 96% confidence interval for the population mean of all bulbs produced by this firm.
**Solution:**
To find a 96% confidence interval for the population mean, we use the formula for the confidence interval of the mean when the population standard deviation is known:
\[ \bar{X} \pm Z \left( \frac{\sigma}{\sqrt{n}} \right) \]
Where:
- \(\bar{X}\) is the sample mean
- \(Z\) is the Z-value from the standard normal distribution corresponding to the desired confidence level
- \(\sigma\) is the population standard deviation
- \(n\) is the sample size
Given:
- Sample mean (\(\bar{X}\)) = 780 hours
- Population standard deviation (\(\sigma\)) = 40 hours
- Sample size (\(n\)) = 30
- Confidence level = 96%
First, we need to find the Z-value for a 96% confidence level. The 96% confidence level corresponds to a Z-value of approximately 2.05 (You can find this value in standard Z-tables or using software/tools for more accuracy).
Now, we calculate the margin of error:
\[ \text{Margin of Error} = Z \left( \frac{\sigma}{\sqrt{n}} \right) = 2.05 \left( \frac{40}{\sqrt{30}} \right) \approx 14.97 \]
Next, we calculate the confidence interval:
\[ \text{Confidence Interval} = \bar{X} \pm \text{Margin of Error} \]
\[ \text{Confidence Interval} = 780 \pm 14.97 \]
Therefore, the 96% confidence interval for the population mean is:
\[ 780 - 14.97 \leq \mu \leq 780 + 14.97 \]
\[ 765.03 \leq \mu \leq 794.97 \]
So, we are 96% confident that the population mean life of all light bulbs produced by this firm is between 765.03 hours and 794.97 hours.
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