A NAPA Auto Parts supplier wants information about how long car owner plan to keep their cars. A random sample of 35 car owners results in a sample average of 7.01 years and a standard deviations of 3.74 years. Assume that the sample is drawn from a normally distributed population. Find a 95% confidence interval estimate of the population mean • P- PARAMETER o Describe the parameter in context. This should be a complete sentence • A- ASSUMPTIONS o Are we allowed to construct an interval and why? • N- NAME THE INTERVAL o State what command you will be using the compute the interval along with the values you need. • 1 - INTERVAL CALCULATION o Find the interval C- CONCLUSION

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### Confidence Interval Estimation for Population Mean

A NAPA Auto Parts supplier wants information about how long car owners plan to keep their cars. A random sample of 35 car owners results in a sample average of 7.01 years and a standard deviation of 3.74 years. Assume that the sample is drawn from a normally distributed population.

Find a 95% confidence interval estimate of the population mean.

### Step-by-Step Approach: PANIC

#### **P – PARAMETER**
Describe the parameter in context. This should be a complete sentence.
- **Context**: The parameter is the average number of years that car owners plan to keep their cars. 

#### **A – ASSUMPTIONS**
Are we allowed to construct an interval and why?
- **Justification**: We can construct a confidence interval since the sample size is 35, which is greater than 30, making the Central Limit Theorem applicable. Additionally, it is given that the sample is drawn from a normally distributed population.

#### **N – NAME THE INTERVAL**
State what command you will be using to compute the interval along with the values you need.
- **Command**: We will use the formula for a confidence interval for the population mean:
\[ \bar{x} \pm t^* \left(\frac{s}{\sqrt{n}}\right) \]
where \( \bar{x} \) is the sample mean, \( s \) is the sample standard deviation, \( n \) is the sample size, and \( t^* \) is the critical value from the t-distribution for 95% confidence.

#### **I – INTERVAL CALCULATION**
Find the interval.
1. **Sample Mean (\( \bar{x} \))**: 7.01 years
2. **Sample Standard Deviation (\( s \))**: 3.74 years
3. **Sample Size (\( n \))**: 35
4. **Degrees of Freedom (df)**: \( n - 1 = 34 \)
5. **Critical Value (\( t^* \))**: The critical t-value for 34 degrees of freedom at a 95% confidence level can be found using a t-table or calculator, approximately 2.032.

Using the formula:
\[ 7.01 \pm 2.032 \left(\frac{3.74}{\sqrt{35}}\right) \]
Transcribed Image Text:### Confidence Interval Estimation for Population Mean A NAPA Auto Parts supplier wants information about how long car owners plan to keep their cars. A random sample of 35 car owners results in a sample average of 7.01 years and a standard deviation of 3.74 years. Assume that the sample is drawn from a normally distributed population. Find a 95% confidence interval estimate of the population mean. ### Step-by-Step Approach: PANIC #### **P – PARAMETER** Describe the parameter in context. This should be a complete sentence. - **Context**: The parameter is the average number of years that car owners plan to keep their cars. #### **A – ASSUMPTIONS** Are we allowed to construct an interval and why? - **Justification**: We can construct a confidence interval since the sample size is 35, which is greater than 30, making the Central Limit Theorem applicable. Additionally, it is given that the sample is drawn from a normally distributed population. #### **N – NAME THE INTERVAL** State what command you will be using to compute the interval along with the values you need. - **Command**: We will use the formula for a confidence interval for the population mean: \[ \bar{x} \pm t^* \left(\frac{s}{\sqrt{n}}\right) \] where \( \bar{x} \) is the sample mean, \( s \) is the sample standard deviation, \( n \) is the sample size, and \( t^* \) is the critical value from the t-distribution for 95% confidence. #### **I – INTERVAL CALCULATION** Find the interval. 1. **Sample Mean (\( \bar{x} \))**: 7.01 years 2. **Sample Standard Deviation (\( s \))**: 3.74 years 3. **Sample Size (\( n \))**: 35 4. **Degrees of Freedom (df)**: \( n - 1 = 34 \) 5. **Critical Value (\( t^* \))**: The critical t-value for 34 degrees of freedom at a 95% confidence level can be found using a t-table or calculator, approximately 2.032. Using the formula: \[ 7.01 \pm 2.032 \left(\frac{3.74}{\sqrt{35}}\right) \]
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