A mechanic sells a brand of automobile tire that has a life expectancy that is normally distributed, with a mean life of 36,000 miles and a standard deviation of 2700 miles. He wants to give a guarantee for free replacement of tires that don't wear well. How should he word his guarantee if he is willing to replace approximately 10% of the tires? Click here to view page 1 of the standard normal distribution table. Click here to view page 2 of the standard normal distribution table. Tires that wear out by miles will be replaced free of charge. (Round to the nearest mile as needed.)

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### Tire Replacement Guarantee: Practical Application of Normal Distribution

A mechanic sells a brand of automobile tire that has a life expectancy that is normally distributed, with a mean life of 36,000 miles and a standard deviation of 2700 miles. He wants to give a guarantee for free replacement of tires that don’t wear well. How should he word his guarantee if he is willing to replace approximately 10% of the tires?

#### Instructions:

To find the mileage threshold at which 10% of tires wear out prematurely (and are thus eligible for replacement), follow these steps using the standard normal distribution:

1. **Consult the Standard Normal Distribution Table:** 
   - [Click here to view page 1 of the standard normal distribution table.](#)
   - [Click here to view page 2 of the standard normal distribution table.](#)

2. **Determine the Z-Score for the 10th Percentile:**
   - Locate the z-score that corresponds to the cumulative probability of 0.10.

3. **Calculate the Respective Mileage:** 
   - Use the mean (36,000 miles) and standard deviation (2700 miles) to convert the z-score into the mileage value.

#### Guarantee Statement

Tires that wear out by ____ miles will be replaced free of charge.  
*(Round to the nearest mile as needed.)*

---

### Explanation of the Concepts and Tools

#### Standard Normal Distribution Table:
The table provides the cumulative probability associated with each z-score in a standard normal distribution (mean = 0, standard deviation = 1). These tables allow us to determine the probability that a sample falls below a particular z-score.

#### Calculating Z-Scores:
Z-scores indicate how many standard deviations an element is from the mean. They are calculated as follows:
\[ Z = \frac{(X - \mu)}{\sigma} \]
Where:
- \( X \) is the value in the normal distribution.
- \( \mu \) is the mean of the distribution.
- \( \sigma \) is the standard deviation of the distribution.

By finding the z-score corresponding to the 10th percentile and converting it using the formula above, you can determine the mileage at which the mechanic should offer free replacements.
Transcribed Image Text:### Tire Replacement Guarantee: Practical Application of Normal Distribution A mechanic sells a brand of automobile tire that has a life expectancy that is normally distributed, with a mean life of 36,000 miles and a standard deviation of 2700 miles. He wants to give a guarantee for free replacement of tires that don’t wear well. How should he word his guarantee if he is willing to replace approximately 10% of the tires? #### Instructions: To find the mileage threshold at which 10% of tires wear out prematurely (and are thus eligible for replacement), follow these steps using the standard normal distribution: 1. **Consult the Standard Normal Distribution Table:** - [Click here to view page 1 of the standard normal distribution table.](#) - [Click here to view page 2 of the standard normal distribution table.](#) 2. **Determine the Z-Score for the 10th Percentile:** - Locate the z-score that corresponds to the cumulative probability of 0.10. 3. **Calculate the Respective Mileage:** - Use the mean (36,000 miles) and standard deviation (2700 miles) to convert the z-score into the mileage value. #### Guarantee Statement Tires that wear out by ____ miles will be replaced free of charge. *(Round to the nearest mile as needed.)* --- ### Explanation of the Concepts and Tools #### Standard Normal Distribution Table: The table provides the cumulative probability associated with each z-score in a standard normal distribution (mean = 0, standard deviation = 1). These tables allow us to determine the probability that a sample falls below a particular z-score. #### Calculating Z-Scores: Z-scores indicate how many standard deviations an element is from the mean. They are calculated as follows: \[ Z = \frac{(X - \mu)}{\sigma} \] Where: - \( X \) is the value in the normal distribution. - \( \mu \) is the mean of the distribution. - \( \sigma \) is the standard deviation of the distribution. By finding the z-score corresponding to the 10th percentile and converting it using the formula above, you can determine the mileage at which the mechanic should offer free replacements.
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