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
Section: Chapter Questions
Problem 1P
icon
Related questions
Topic Video
Question
100%

4. Please help me answer this including the z-table.

**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.
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.
Expert Solution
trending now

Trending now

This is a popular solution!

steps

Step by step

Solved in 2 steps with 1 images

Blurred answer
Knowledge Booster
Research Design Formulation
Learn more about
Need a deep-dive on the concept behind this application? Look no further. Learn more about this topic, statistics and related others by exploring similar questions and additional content below.
Similar questions
Recommended textbooks for you
MATLAB: An Introduction with Applications
MATLAB: An Introduction with Applications
Statistics
ISBN:
9781119256830
Author:
Amos Gilat
Publisher:
John Wiley & Sons Inc
Probability and Statistics for Engineering and th…
Probability and Statistics for Engineering and th…
Statistics
ISBN:
9781305251809
Author:
Jay L. Devore
Publisher:
Cengage Learning
Statistics for The Behavioral Sciences (MindTap C…
Statistics for The Behavioral Sciences (MindTap C…
Statistics
ISBN:
9781305504912
Author:
Frederick J Gravetter, Larry B. Wallnau
Publisher:
Cengage Learning
Elementary Statistics: Picturing the World (7th E…
Elementary Statistics: Picturing the World (7th E…
Statistics
ISBN:
9780134683416
Author:
Ron Larson, Betsy Farber
Publisher:
PEARSON
The Basic Practice of Statistics
The Basic Practice of Statistics
Statistics
ISBN:
9781319042578
Author:
David S. Moore, William I. Notz, Michael A. Fligner
Publisher:
W. H. Freeman
Introduction to the Practice of Statistics
Introduction to the Practice of Statistics
Statistics
ISBN:
9781319013387
Author:
David S. Moore, George P. McCabe, Bruce A. Craig
Publisher:
W. H. Freeman