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MATLAB: An Introduction with Applications
6th Edition
ISBN:9781119256830
Author:Amos Gilat
Publisher:Amos Gilat
Chapter1: Starting With Matlab
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### Confidence Interval for Average Typing Speed of Secretarial School Graduates

**Problem Statement:**
A random sample of 12 graduates of a certain secretarial school typed an average of 82.2 words per minute with a standard deviation of 7.1 words per minute. Assuming a normal distribution for the number of words typed per minute, determine a 99% confidence interval for the average number of words typed by all graduates of this school.

**Resources Provided:**
- [Page 1 of the standard normal distribution table](#)
- [Page 2 of the standard normal distribution table](#)
- [Page 1 of the table of critical values of the t-distribution](#)

**Confidence Interval Calculation:**
The confidence interval is given by:

\[ \bar{x} \pm t \left( \frac{s}{\sqrt{n}} \right) \]

Where:
- \(\bar{x}\) is the sample mean
- \(t\) is the t-value from the t-distribution for \(n-1\) degrees of freedom and the specified confidence level
- \(s\) is the sample standard deviation
- \(n\) is the sample size

**Formula for this Problem:**
\[ 82.2 \pm t_{0.005, 11} \left( \frac{7.1}{\sqrt{12}} \right) \]

**Confidence Interval Result:**
The confidence interval is [  ,  ] (Round to two decimal places as needed.)

**Interactive Component:**
Enter your answer in the edit fields and then click **Check Answer**.

[Check Answer Button]

#### Additional Instructions:
- Use the provided links to access the necessary tables for standard normal distribution and t-distribution critical values.
- Ensure your final answer is rounded to two decimal places.

**Graphical Representation:**
While the image does not contain an explicit graph or diagram, the values needed to complete the calculation (standard deviation, sample mean, sample size, and confidence level) are provided.

---

**Note for Users:**
This exercise demonstrates how to compute a confidence interval for a sample mean when the population standard deviation is unknown and the sample size is small (n < 30). This requires the use of the t-distribution, a critical concept in inferential statistics.
Transcribed Image Text:### Confidence Interval for Average Typing Speed of Secretarial School Graduates **Problem Statement:** A random sample of 12 graduates of a certain secretarial school typed an average of 82.2 words per minute with a standard deviation of 7.1 words per minute. Assuming a normal distribution for the number of words typed per minute, determine a 99% confidence interval for the average number of words typed by all graduates of this school. **Resources Provided:** - [Page 1 of the standard normal distribution table](#) - [Page 2 of the standard normal distribution table](#) - [Page 1 of the table of critical values of the t-distribution](#) **Confidence Interval Calculation:** The confidence interval is given by: \[ \bar{x} \pm t \left( \frac{s}{\sqrt{n}} \right) \] Where: - \(\bar{x}\) is the sample mean - \(t\) is the t-value from the t-distribution for \(n-1\) degrees of freedom and the specified confidence level - \(s\) is the sample standard deviation - \(n\) is the sample size **Formula for this Problem:** \[ 82.2 \pm t_{0.005, 11} \left( \frac{7.1}{\sqrt{12}} \right) \] **Confidence Interval Result:** The confidence interval is [ , ] (Round to two decimal places as needed.) **Interactive Component:** Enter your answer in the edit fields and then click **Check Answer**. [Check Answer Button] #### Additional Instructions: - Use the provided links to access the necessary tables for standard normal distribution and t-distribution critical values. - Ensure your final answer is rounded to two decimal places. **Graphical Representation:** While the image does not contain an explicit graph or diagram, the values needed to complete the calculation (standard deviation, sample mean, sample size, and confidence level) are provided. --- **Note for Users:** This exercise demonstrates how to compute a confidence interval for a sample mean when the population standard deviation is unknown and the sample size is small (n < 30). This requires the use of the t-distribution, a critical concept in inferential statistics.
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